V Boudry

G Fisk

R E Frey

F Gaede

C Hast

J Hauptman

K Kawagoe

L Linssen

R Lipton

W Lohmann

T Matsuda

T Nelson

R Pöschl

E Ramberg

F Sefkow

M Vos

M Wing

J Yu

Summary of the Linear Collider Testbeam Workshop "LCTW09"

published or not. The documents may come

L'archive ouverte

Executive summary

The next major worldwide project in high energy particle physics will be a linear electron positron collider at the TeV scale. This machine will complement and extend the scientific results of the LHC currently operated at CERN. The most advanced proposal for such a machine is the International Linear Collider (ILC) which will be operated at centre-of-mass energies between 90 GeV and 1 TeV. The experimentation at this machine could start around the year 2020. Introductions to the concept of the ILC and to the alternative for higher energies CLIC, short for Compact LInear Collider concept, can be found elsewhere [START_REF]ILC Global Design Effort and World Wide Study[END_REF][START_REF] Battaglia | [END_REF].

Beams tests are necessary for detector concepts to validate their design and gain valuable operating experience. At the same time they are an optimal opportunity to train young physicist on real data. In November 2009, 40 experts (two from Asia, five from North America and the rest from Europe) met at the Laboratoire de l'Accélérateur Linéaire (LAL) at Orsay to review the needs for future beam tests for the R&D on detectors [3]. The goal of this workshop was to collect the needs and to coordinate the activities of the various collaborations active in the field: CALICE, FCAL, SiD as well as groups working on the dual readout technology on calorimetry, LCTPC on gaseous tracking as well as SiLC for the various silicon tracking devices. Representatives of the current major test beam facilities, CERN, DESY and Fermilab, presented their sites and actively took part in the discussions. Many other facilities available in the world were discussed: J-Parc, IHEP Bejing, Tohoku, KEK in Asia, IHEP/Protvino, Dubna in Russia, and it was noticed that SLAC would restore test beams and create a new facility in its End Station A by 2010. The successful beam test efforts prior to the Letters of Intent (LOI) for detectors [START_REF]The International Large Detector; Letter of Intent[END_REF][START_REF] Aihara | [END_REF][START_REF]Fourth Concept Group[END_REF] were reviewed followed by discussions on what is needed to improve these test beams for the next phase. This document covers the years 2010-2013 which to a large extent coincides with the preparation of the Detector Baseline Document (DBD) in which mature detector technologies are to be presented. The beam test efforts have to support this goal. Large scale systems of all detector components are expected to be tested in this phase. The successful conduction of the beam tests is naturally vital for a well founded document. Apart from the fact that the detector developers have to be ready in time, the community has to make sure that enough beam time is available, in particular in the period 1/2011 -2/2012 in which most of the activities described in this note can be anticipated. The needs of the linear collider detector community in terms of particles comprises high and low energy electron as well as high and low energy hadron beams. In addition to the beam lines, the linear collider detector R&D requires specific equipment such as large-bore high-field magnets (up to 6 T). The Table 1 gives a general overview on the activities planned by the various detector components. Another important issue of the detector R&D is to find the optimal balance between high beam rates to conduct physics motivated studies and the fact that e.g. the readout electronics is primarily designed for low rates as in initial operation expected at a linear collider. While the priority is clearly to be given to the availability of test beams, the establishment of a dedicated ILC beam structure would render the results more applicable to prospects on the operation at the ILC. This would be particularly true for the general time structure, i.e. "macro-structure" of the beam. This means that a relatively short pulse of about 1 ms is followed by a longer interval of up to 199 ms without beam. All the R&D groups would make use of such a possibility to test their hardware under the most realistic conditions. There would be no strong requirement to reproduce the micro-structure of the ILC beams. The community encourages the site operators to continue efforts to establish an ILC like beam structure. Given the limited time line and manpower situation the LC Detector community will establish a light coordination of the beam test activities to foster synergies and avoid overlaps in terms of beam times and facilities.

The activities of the past and the challenging program of the future have been acknowledged in Europe by the recent approval of the AIDA project. The AIDA project [7] was presented as a proposal for Integrating Activity under the 7th framework of the European Union. This funding instrument is largely based on the "I3" (integrated infrastructure initiatives) under which EUDET [8] was funded. The objectives are (a) to provide a wider and more efficient access to, and use of the existing research infrastructures in Europe and (b) better integration of the way research infrastructures operate, and fostering joint development in terms of capacity and performance. AIDA involves most of the linear collider detector R&D community that participated in EUDET. It moreover includes a strong participation from the institutes involved in the upgrades of the LHC detectors, in that of the B-factories and accelerator-based neutrino experiments. At the time of writing, AIDA was in the negotiation phase after the EU had proposed to fund the proposal with 8 million euro (compared to the 10 million requested from the EU in the original proposal). In the proposal common infrastructure for the characterisation of new detector prototypes is foreseen. It should be emphasised that the programs were and are open for participation of non-european partners in the actual projects.

World wide linear collider beam test coordination and review

Efforts on the International Linear Collider increased after the creation of the Global Design Effort (GDE) in 2004. Along with the global effort on the accelerator front, many detector development groups intensified their activities and their need for beam tests rose. These efforts were, however, fragmented and not coordinated. Given the anticipated intensity of beam test efforts in the coming few years, it was necessary for the community and the facilities to be able to provide necessary beam capabilities to detector R&D groups. The facilities, however, needed to know what the requirements for the community are. As an effort to convey the upcoming needs, the calorimeter and muon R&D groups have put together a road map document to FNAL in 2005, following a presentation to the Physics Advisory Panel (PAC). This document [START_REF] Yu | ILC Calorimeter and Muon Detector R&D Community, International Linear Collider Calorimeter/Muon Detector Test Beam Program (A Planning Document for Use of Meson Test Beam Facility at Fermilab)[END_REF] and the need for more concerted effort led to the implementation of a working group structure and prompted the need for a world-wide ILC test beam workshop to collect and compile the requirements of most, if not all, R&D groups within the community. This was to provide a forum to share ideas and needs between many different groups within the LC community and to make sure that the limited facilities can be used effectively.

LC Test Beam Workshop 2007 (IDTB07) at FNAL

The LCTW09 as summarised in this document is the second workshop of this kind. The first workshop on linear collider beam tests, called IDTB07, was held at FNAL in Jan. 2007. As a result of three days of presentations and discussions at IDTB07, the following requirements were identified: Large bore, high field magnet (up to 5T); The DESY facility gave a 'home' to the TPC activities which could then establish the infrastructure needed to pursue the R&D at a single place.

Beyond the activities above, the various sites, i.e. CERN, DESY, FNAL, SLAC and KEK, offered beam time to smaller yet very important activities by the vertex, silicon tracking and muon detector communities.

The detector R&D community would like to take the opportunity here to express their acknowledgement and gratitude for the effort made by the test beam sites.

The beam test activities resulted in a number of scientific results which can be viewed on the web-pages of the different projects.

3 Subdetector beam test plans

Calorimeter

As will be outlined in this section the calorimeters may put the highest demands in terms of space and availability of beam test areas. Many projects feature prototypes of about 1 m 3 and need high statistics for the conduction of physics programs during the beam test campaigns.

CALICE plans

An overview of past, present and future CALICE calorimeter prototypes is available in Table 2. For details on the CALICE program, the reader is referred to [START_REF]CALICE Report to the DESY Physics Research Committee[END_REF]. Table 2: Overview of calorimeter prototypes having been or to be operated by the CALICE collaboration.

Each project has developed or is developing prototype(s) classified as physics, used to demonstrate the physics performances of the technique, or technological, used to study the solutions to the technological constraints arising from the integration in a large ILC detector 1 , or both. The Digital ECAL (DECAL) technique has only been studied in small devices and no full-scale physics prototype has been built. As this project depended on UK funding which has now been cancelled, it is unlikely such a prototype will be constructed in the foreseeable future.

Two generation of DAQ system have been developed: the first version, more specifically dedicated to physics prototypes, has been running for a few years. The second version, suited for technological prototypes and handling the readout of a large quantity of channels digitised in the detectors, is at the end of its development phase. More details are given in Section 3.4.

Physics prototypes

The years 2010-11 will see the finalisation of the main physics prototype phase. A physics prototype of a digital hadron calorimeter (DHCAL) based on thin RPCs and 1 × 1 cm 2 cells, will be completed in the first half of 2010. As for previous beam tests including the analogue hadron calorimeter (AHCAL), besides standalone data taking, there will be data taking in combination with the physics prototype of the electromagnetic silicon tungsten calorimeter (SiW ECAL) and the Tail Catcher and Muon tracker (TCMT).

Including commissioning and calibration phases altogether, 14 weeks of test beam time will be requested from FNAL. Within these 14 weeks, CALICE should be the primary beam user for about 8 weeks. The other 6 weeks are devoted to the setup of the experiment in parasitic running mode. The physics program to be conducted is largely similar to the corresponding data taking in the years 2006-09 with the AHCAL. In the combined running, the emphasis will be put on energy ranges in which it is expected to see signals in the electromagnetic part and the hadronic part (plus tail catcher). In the standalone running low energy hadrons and electrons are also to be collected. Priorities will have to be defined later on but the data which were already taken give good guidelines. It is also envisaged to replace a few layers of the DHCAL with GEMs as sensitive detectors. This may happen in 2011.

A new initiative, dubbed W-HCAL, has been started within CALICE in order to study the properties of tungsten as absorber material, primarily for a compact HCAL at a multi-TeV collider. A versatile structure, featuring forty 16 mm-thick tungsten-alloy absorbers, is foreseen. Tests with existing scintillator layers are planned for end of 2010 and 2011 at CERN. Tests with gaseous insert and second generation scintillator as they become available.

Technological prototypes

The CALICE collaboration is entering a new phase of R&D in which readout technologies and mechanical designs meet many requirements of the operation in a detector for a Linear Collider. Several groups of the collaboration are already quite advanced and new full scale prototypes are expected towards the end of 2010. The finalisation of these prototypes will be preceded by a number of smaller beam test efforts which will allow for maturing the newly developed technologies. Examples for these test beam efforts are:

Beam tests with 1 m 2 units of the technical prototype of the SDHCAL (both RPC and µMegas variants).

The AHCAL conducted an initial small scale beam test at the beginning of 2010 to prepare for electronics commissioning, to be followed by a so-called horizontal test towards the end of 2010 and a vertical test in 2011. This means the available equipment will be arranged to allow for the measurement of electromagnetic showers.

The Si-W ECAL is planning to make tests with single ASU towards the beginning of 2011 in a beam test with electrons.

It has to be stressed that the primary goal of these prototypes is to study technological solutions for the calorimetry at the ILC. The strategy for the coming years should take this into account. Here the main keywords are power pulsing, with a duty-cycle of typically 1 %, and limited depth of the buffers in the front end electronics. Hence the provided particle rates should not exceed 1 kHz during a spill. This is even more limited for RPCs, due to their comparatively large recovery time, requiring rates 0.1 kHz.

In addition to the pure technological issues a physics program is to be pursued. Derived from those of the physics prototypes, taking the technical constraints into account, it requires the operators of beam test sites to actively respond to the needs of the CALICE (LC) beam test data taking at an very early stage. As it is foreseeable that potential high statistics physics runs will take a considerable amount of time, this will require the deployment of remote control at the experimental sites. As some prototypes may use flammable gas, the topic of safety will have to be addressed at a very early stage.

A first large scale beam test with a fully equipped technical prototype of an SDHCAL can be expected towards spring 2011. It is still to be clarified in what proportion this cubic meter prototype will be equipped with the two technologies under study, namely using Glass RPCs or µMegas as sensitive devices. This is currently being reviewed on the basis of experience gained with the two technologies by laboratory studies and during test beam campaigns of the year 2009.

Ideally, the SDHCAL will be joined by an SiW ECAL technological prototype by the end of 2011. The running of an AHCAL technical prototype alone and together with the SiW ECAL technical prototype is to follow. During the year 2010 mechanical interfaces between the different detector types will have to be defined. More generally the year 2010 is to be used to integrate the detector components with the newly developed DAQ systems in order to provide an efficient data taking.

The program requires a high availability of beam test areas. The CALICE management and the CALICE TB together with the corresponding ILC R&D panels will work out until summer 2010 whether ILC detector R&D can occupy consecutively beam test areas for a time of two or more years starting with the beginning of 2011. Such a high availability of beam test areas would also allow for an easier conduction of smaller beam test programs as for example with the DECAL. In addition the infrastructure would facilitate the testing of a prototype for the electromagnetic calorimeter based on scintillating tiles (ScW ECAL) of which one layer can be expected towards the end of 2012. Finally, technological prototype layers with timing capabilities should also be used in a beam test with a tungsten absorber structure.

SiD ECAL

The silicon tungsten ECAL developed specifically for SiD features 30 longitudinal sampling layers composed of hexagonal high resistivity silicon wafers divided in small hexagonal cells (13 mm 2 ). The readout of 1024 channels is performed by a single KPiX chip bump-bonded directly on the wafer. The chip is connected to the DAQ by flat polyimide cables. The R&D on components is almost completed and a compact stack prototype (30 layers of one wafers, interleaved with 15 × 15 cm 2 tungsten alloy absorbers) is being built and should be ready for test beam in beginning of 2011.

The ideal test beam for initial test is a 5-10 GeV (or more) electron beam, well localised and controllable, with a LC-like time structure (for KPiX electronics). A small number of electrons (mean of ∼ 1 -2) per bunch is a must. Such a beam is possibly available at SLAC, with a low rate (< 60 Hz).

The data taking is planned for 2011, preferably at SLAC if a beam exists by then (the current expectation is to have SLAC test beam available around winter 2011). The possibility to realise combined tests with a HCAL prototype with a hadron beam in 2012-13, needs to be evaluated.

SiD Muons

The muon system of the SiD concept [START_REF] Aihara | [END_REF] will be placed after a thin (5 λ I ) calorimeter, the solenoid coil and cryostat (1.3 λ I ) and is therefore crucial to measure leakage of highly energetic and late-developing showers. It features a total detector area of about 6000 m 2 on 14 layers for a total number of channels of 50K (if single ended) to 100K (if dual readout).

The main criteria of choice are the cost, the ease of shape adaptation and performance and reliability. The need to operate inside the return yoke adds the following: insensitivity to magnetic field, space economy for the readout system (cables, FE, etc), reliability and slow ageing.

Two technologies are considered:

RPC based (baseline) Uses a variant of the KPiX readout chip, double gap Bakelite RPCs operating in the avalanche mode are or will be tested. This effort benefits from synergy with the DHCAL (readout ASIC) and a long experience in various experiments (BaBar, Opera, BES-III, . . . ) but some ageing and reliability issues have still to be clarified, using cosmic ray test stands with radioactive sources for tests of new Beijing Bakelite manufactured RPCs for used in the BES III and Daya Bay muon systems. Since RPCs using this material have achieved acceptable dark noise rates without linseed oil coating, these RPCs look promising [START_REF] Lu | [END_REF], but ageing effects have not been thoroughly studied.

Scintillator based (alternative) : wave-length-shifting fibre readout of cheap extruded scintillator coupled with new (and potentially) low-cost Si-based avalanche photo-diodes (Pixelated Photon Detectors or PPDs, also dubbed SiPMs) make the scintillator alternative progressively more competitive if long strips of up to 6 m are feasible. Prototypes featuring 256 scintillator strips and Multi Anode PMTs have been tested in the Fermilab Meson Test Beam Facility (MTBF), see Section 4.4. A small sample of prototype were tested in 2008 at the Fermilab MTBF with a new type of SiPM, developed by FBK-IRST (Trento, Italy) to match the circular cross section of WLS fibre and have also shown good results. The main objectives of the MTBF tests have been to measure an expected increase in number of photo-electrons due to the increased quantum efficiency of the PPDs and to use the spontaneous release of photo-electrons that is normally called "noise" to measure the gain vs. bias voltage and thereby establish a calibration without special additional equipment.

For an overview on the results of the tests described before see e.g. [START_REF] Rubinov | [END_REF].

The short term plans are for RPCs at SLAC to be read out using multiple KPiX chips in cosmic-ray test stands with BaBar and Chinese RPCs (Henry Band). In a separate parallel cosmic ray setup at Princeton, Chang-guo Lu and colleagues will test new Chinese RPCs manufactured commercially. A major objective of the cosmic ray tests is the measurement of efficiency in a high background artificially created with radioactive sources.

The prototype scintillator strip tests will benefit from new readout electronics cards optimised for SiPMs that will allow verification of the MINOS determined attenuation length and the measurement of single ended readout efficiency for strips up to 6 m to qualify SiPMs in test beam conditions. Northern Illinois University has made recent test beam measurements of PPDs directly coupled to scintillator. This technology, if successful, would make the tail-catcher/muon tracker (TCMT) a realistic possibility.

The requirements on the beam test setup for prototypes of the muon system are light, with limited place and narrow beam of mip (up to now a well defined beam spot (1 cm) of 120 GeV protons at 10 2 -10 4 p/sec is enough). These conditions are perfectly met at the MTBF at FNAL. There, the set-up can either be easily shared other R&D test setup or serve as a complementary device for e.g. a calorimeter prototype such as the CALICE ones.

In the longer term for the ILC there will be more development of readout electronics (ASIC), SiPM, measurements to improve optical coupling of fibres to detectors, systems tests with improved DAQ and analysis software and the evolution of tests with calorimetry and tracking detectors. And there is the hope that there will be improved tracking at MTBF to better define beam parameters for individual particles.

DREAM and dual readout calorimetry

The DREAM collaboration has tested dual-readout calorimeters in the H4 beam (North Area) at CERN from 2004 through 2009 [START_REF]Dual-Readout Calorimetry for High-Quality Energy Measurements[END_REF]. These tests started with the small 1 kt DREAM module (consisting of Cu tubes filled with scintillating and clear fibres), and resulted in publications on basic responses and resolutions [START_REF]Dual-Readout Calorimetry for High-Quality Energy Measurements[END_REF](a-c), shower shapes [START_REF]Dual-Readout Calorimetry for High-Quality Energy Measurements[END_REF] (d,h), scintillation-Čerenkov separation in fibres [START_REF]Dual-Readout Calorimetry for High-Quality Energy Measurements[END_REF](e), and the response to and role of neutrons in a dual-readout fibre calorimeter [START_REF]Dual-Readout Calorimetry for High-Quality Energy Measurements[END_REF](f,l).

Further test included dual-readout in crystals: Lead Tungstate (PWO, or PbWO 4 ) single crystals [START_REF]Dual-Readout Calorimetry for High-Quality Energy Measurements[END_REF](g,i,j,k,n,p), extending to arrays of PWO and BGO crystals [START_REF]Dual-Readout Calorimetry for High-Quality Energy Measurements[END_REF](m,o), and finally including a full mock-up of a crystal-plus-fibre calorimeter with 11 λ int depth [START_REF]Dual-Readout Calorimetry for High-Quality Energy Measurements[END_REF](o).

The DREAM collaboration has continued testing in the H8 beam at CERN in July 2010 and will continue for 3-to-5 years exploring the ultimate hadronic energy resolution attainable in dual-readout calorimeters.

The measurements taken in the one-week H8 test run in July 2010 included (a) direct comparisons of BGO and BSO crystals; (b) measurements of the response variations among eight doped PWO crystals of nominal identical manufacture; (c) tests of an "anti-Čerenkov" PMT; (d) tests of a Pb-quartz plate module; and, (e) direct measurement of polarised Čerenkov light in a BSO crystal. These studies will be published soon.

Finally, a large dual-readout fibre module with an expected 1 % average leakage is being built to complement and complete the measurements made with the small 1 kt DREAM module. We also expect to build a crystal "em" module to test in conjunction with the larger fibre module. These activities are scheduled for the H8 beam at CERN.

Forward calorimetry

The FCAL collaboration [15] develops technologies for the instrumentation of the very forward region of detectors at the ILC or CLIC collider. For the validated detector concepts ILD [START_REF]The International Large Detector; Letter of Intent[END_REF] and SiD [START_REF] Aihara | [END_REF] two calorimeters are foreseen: LumiCal for a precise luminosity measurement and BeamCal for a bunch-by-bunch luminosity and beam-parameter estimate. For the latter the depositions from beamstrahlung pairs in BeamCal are used. For the measurement of the beamstrahlung pair density BeamCal will be supplemented by a pair monitor consisting of a layer of pixel sensors in front of BeamCal.

Both calorimeters extend the detector coverage to low polar angles, potentially important for search experiments using missing momentum as signature. The challenges are high precision shower position measurement in LumiCal, radiation hard sensors for BeamCal, and a fast front-end electronics for both.

The LumiCal dedicated to the precise measurement of the luminosity using Bhabha events. It features 30 tungsten layers of 1 X 0 thickness each, interspersed with very finely segmented silicon sensors. To ensure a precision of the luminosity measurement of 10 -3 , as required from physics, a correspondingly precise shower position measurement is needed. The latter can be translated in severe constraints on the sensor positioning accuracy and the position monitoring of the calorimeters. Due to the relatively high occupancy fast front-end electronics and digitisation is needed;

The mechanical structure of the BeamCal and Pair Monitor is similar to LumiCal. However, due to the large depositions from beamstrahlung pairs, about 10 Mgy/yr for the sensors near the beam-pipe, radiation hard sensors are needed. For this purpose large area GaAs sensors are under development in collaboration with partners in Russia. Also CVD diamond sensors are investigated. The BeamCal has to be readout after each bunch crossing. In addition a fast signal added up from groups of pads is foreseen for beam-tuning. Specialised fast front-end electronics is under development.

The Pair Monitor is a pixel sensor covering the front area of BeamCal. SoI technology is chosen with readout integrated in the silicon wafer;

The system may be completed by a GamCal, 100 m downstream of the detector, is considered to assist beam-tuning.

To investigate the radiation hardness of several sensor materials a special test-beam program is ongoing.

Major components of BeamCal and LumiCal, as sensors, flexible PCB for signal transport, front-end ASICs and ADC ASICs are available as prototypes and tested separately. Just now a full system comprised by sensor prototypes and an acquisition chain is being mounted. First measurements in the 5 GeV electron test-beam at DESY are foreseen in August 2010, using the EUDET telescope. Test-beam requirements:

For irradiation studies electron beams with currents between 10 and 100 nA and around 10-40 MeV energy are appropriate. Such beams are available, and used, at the sDALINAC at the Technical University in Darmstadt, and at the ELBE linac at Forschungszentrum Dresden-Rossendorf (FZD);

For performance studies of fully assembled sensor planes the 4 GeV electron beam with a beam intensity of a few 10 s -1 seems sufficient. Such a beam is available at DESY. In 2010 two weeks are scheduled. Similar campaigns are planned in the following 3 years; Within AIDA the plan is to prepare a prototype of a calorimeter sector. To test its performance a electron beam with energies comparable with Linear Collider beam energies, as available e.g. at CERN, will be needed. This program is foreseen to start in 2012.

Summary on tentative sites and special requirements

The beam test campaigns for the CALICE physics prototypes will be conducted initially at FNAL in 2010 with physics prototypes and continued at CERN in 2011 with technological ones. The natural preferred site for the beam tests to be conducted with the technological prototypes is CERN since most of the R&D groups involved in these prototypes are based in Europe. As it is currently however difficult to predict fully the availability of the CERN facilities, FNAL remains a serious option for a test beam site. The prototypes of the CALICE collaboration will not need a dedicated ILC like beam structure. Rather it is desirable to obtain beams with a relatively long flat top with an intensity of not much more than 2 kHz. Such a configuration would is demanded by the layout of the front end electronics which is designed for low occupancy. The validation of the power pulsing technique will however need the availability of a large bore magnet ( > 1 m) with a field strength between 3 and 6 T. In addition beam telescopes with an excellent point resolution should be part of the beam line equipment. The program for muon detectors in the coming years will be based at FNAL and has no special requirements on beam conditions.

Test beams with the prototype of the SiD Ecal will initially be conducted at SLAC with the option to move to FNAL for beam tests with hadrons. The design of the front end electronics for this prototype renders highly desirable the availability of an ILC like beam structure. Low rate beams are mandatory. Test beams with the dual readout technique will be continued at CERN by the DREAM collaboration in the coming 2-3 years. Here, hadron beams up to the highest energies will be needed. In the coming years the forward calorimeters will sustain irradiation tests with low energy but high intensity electrons beams or electrons beams in the few GeV range. These beams are available at Darmstadt, Dresden and DESY. The detector response will be tested with low intensity electrons first at DESY at low energy then at CERN with high energy. All plans of calorimetric and muon systems described before are summarised in Table 3

Silicon tracking

Silicon-based tracking and vertexing is continuing to develop over a broad front. Silicon tracking detectors are well-placed to take advantage of rapid development in silicon technology. These new technologies need to be developed, tested, and validated in test beams. Some technologies, like the DEPFET have already demonstrated resolution less than 5 microns and require high momentum beams and sophisticated telescopes to make proper measurements.

In parallel tracking detectors are testing larger and more realistic "ladder" designs and will need realistic infrastructure such as pulsed power, ILC-like beam structure, magnetic field, and low mass supports.

There is a broad range of work on vertex and tracking technology. Table 4 summarizes some of the technologies being studied for the ILC tracker and vertex detector.

Beam properties and structure

The ILC has a very distinct time structure, with a train of 2820 bunches separated by 337 ns followed by a ≈ 200 ms gap. Such a structure is difficult, but not impossible to mimic in a test beam. Depending on the application, the ILC structure could be mimicked by appropriate trigger electronics or offline analysis. How well this works depends on the details of the detector integration time, time stamping ability, and saturation effects. Many aspects of pulsed powering could be tested independent of beam conditions. History has shown that detailed tests in an environment as close as possible to actual operation are invaluable.

Other beam properties are also important. High energy beams are the only way to unambiguously test detector resolution with minimal multiple scattering. However lower energies are also important to quantify the scattering and validate Monte Carlo models of the detector response. Beams should be able to simulate the rates seen at the inner radius of the vertex detector.

Two-track resolution needs to be studied, both for normal and for glancing incidence. This can be done in a high rate beam, using multiple tracks which pass through the detector within the integration time, or by a secondary target which mimics the interaction vertex. In the case of a secondary target all relevant tracks in the event need to be reconstructed. The momenta also probably have to be measured. This makes for a much more complex setup with a significant magnetic field.

Beam instrumentation

A high quality beam telescope is needed to determine the reference position of the charge particle track. For an unambiguous measurement of the spatial resolution of the device this position must be precisely predicted. Especially for state-of-the-art vertex detector technology this latter requirement poses a severe challenge, requiring sub-micron pointing precision.

Traditionally, much effort of the R&D collaborations is devoted to the construction of precise beam telescopes. The EUDET project [8] offered a precise telescope [START_REF] Roloff | The EUDET high resolution pixel telescope[END_REF] based on MIMOSA monolithic active pixel detectors, hardware to synchronize devices under test and the telescope to the trigger signal as well as a flexible DAQ environment. This infrastructure has attracted a large user community [START_REF] Gregor | Summary of One Year Operation of the EUDET CMOS Pixel Telescope[END_REF].

In AIDA [7] this common infrastructure will be continued and extended. A flexible telescope, combining the precise and thin MIMOSA sensors with fast ATLAS hybrid pixel detectors and/or time-stamping TimePix devices will be built. A CO 2 cooling system will be provided for the test of large-scale prototypes and irradiated devices.

Future applications require devices that combine performance (resolution, read-out speed) with an extreme control of the material in the tracking volume. As more transparent devices are developed the mechanical and thermal design becomes more and more challenging. To characterize the thermo-mechanical properties of prototypes under realistic powering and cooling conditions, a second infrastructure will be developed in AIDA.

Finally, it is envisaged to install silicon µ-strip detectors in front of the highly granular calorimeter infrastructure, described in Section 3.1. These layers aim to provide a precise entry point, thus aiding the analysis of overlapping showers.

A flexible readout system will also be important for testing the large variety of devices being brought to the beams. One example is the CAPTAN system [START_REF] Rivera | CAPTAN : Compact and programmable data acquisition node[END_REF][START_REF] Turqueti | Captan: A Hardware Architecture For Integrated Data Acquisition, Control, And Analysis For Detector Development[END_REF][START_REF] Rivera | A Telescope Using CMS PSI46 Pixels and the CAPTAN for Acquisition and Control over Gigabit Ethernet[END_REF], developed by FERMILAB, and designed a a flexible, FPGA-based readout system for a variety of devices. To date the CAPTAN has been used to read out the BTeV FPIX chip, the CMS pixel chip, the VIKING strip chip, and will be used for the VICTR CMS track trigger chip.

The ALIBAVA system [START_REF] Marco-Hernandez | ALIBAVA Collaboration A portable readout system for microstrip silicon sensors (ALIBAVA)[END_REF] provides a flexible read-out system for µ-strip detectors. Originally developed for the read-out of (irradiated) test structures and small-scale devices (socalled baby detectors), the system is being upgraded to allow multi-module operation with an external trigger, suitable for test beams. A prototype sensor is wire-bonded to a board that includes a Front-End chip (the Beetle of the LHCb VELO detector) and all the ancillary electronics to read-out and control the Front-End. The system is controlled from a PC through a standard USB connection.

Small area trigger can be provided by a version of the VICTR chip, which has a array of 64 1 mm × 100 µm strips with a fast output and maskable pixels. The chip is designed (for LHC upgrade triggering) for a coincidence with a second detector 1-2 mm away.

Gaseous Tracking (2 pages -T. Matsuda)

Physics at the International Linear Collider (ILC) or the Compact Linear Collider (CLIC) will require a detector of high precision. A tracking system of the detector has to achieve a high momentum resolution δ(1/p t ) of a few 10 -5 (GeV/c) -1 [START_REF]ILC Global Design Effort and World Wide Study, International Linear Collider Reference Design Report[END_REF]. This resolution surpasses by 10 times the best momentum resolution achieved by the experiments at LEP. The tracking system should also provide a high tracking efficiency down to a few GeV/c to ensure a good jet-energy measurement by the Particle Flow Algorithm (PFA) in an environment of high beam-induced backgrounds.

To meet with these requirements, a large Time Projection Chamber (TPC) with using Micro Pattern Gas Detectors (MPGD) is proposed as a central tracker of the International Large Detector (ILD) [START_REF]The International Large Detector; Letter of Intent[END_REF]. The ILD TPC is to be located in a large superconducting solenoid of 3.5 T. It measures each track at 220 space points with an rφ spatial resolution of 100 µm or better in the whole drift volume of 2.2 m length. This performance of TPC is only achievable with the MPGD technology [START_REF] Giomataris | [END_REF]18]. At this moment three candidates of MPGD detectors are considered; Bulk MicroMEGAS with resistive anode readout, GEM with narrow pad readout, and, in a somewhat longer time scale, a digital TPC with Ingrid TimePix or a semi-digital TPC using GEM readout by TimePix.

TPC R&D by the LC TPC collaboration

The LC TPC collaboration has been carrying out R&D of the MPGD TPC for ILC (ILD) in three stages; 1. Demonstration phase.

2. Consolidation phase.

Design phase.

At each phase for the last several years, a multitude of beam tests have or will be conducted.

In the demonstration phase (2004-2007) a basic evaluation of the properties of the MPGD gas amplification was made, demonstrating that the requirements for the linear collider (ILD) could be met. For an example, it was shown through beam tests with small TPC prototypes that the rφ space resolution of 100µ could be achieved by both, MicroMEGAS with the resistive anode readout and GEM with the narrow pad readout [START_REF]TPC R&D for an ILC detector[END_REF][START_REF]TPC R&D for a Linear Collider Detector[END_REF].

In the current consolidation phase (2007-), a TPC Large Prototype 1 has been successfully operated (TPC LP1) at the low energy electron 5 GeV/c test beam at DESY, T24-1 [START_REF] Dehmelt | A Large Prototype of a Time Projection Chamber for a Linear Collider Detector, Talk given at TIPP09[END_REF][START_REF] De | Lentdecker for the LC-TPC Collaboration, A Large TPC Prototype for an ILC Detector[END_REF]. The goals of the LP1 beam test are to confirm the results from the demonstration phase for a larger scale TPC, and to show that the excellent momentum resolution is actually achievable for the LC TPC. In 2010 beam tests are performed with the LP1 end-plate equipped with four to seven MPGD modules, and a new TPC tracking code for non-uniform magnetic field is under development. In this phase, in addition to the development of the different MPGD TPC readout modules, basic engineering issues for the LC TPC are studied. Good examples are the construction of a thin LP1 field cage and the development of a low noise, high-density TPC pad readout electronics using S-ALTRO [START_REF] Musa | Prototype compact readout system[END_REF].

Currently the collaboration is entering the design phase (2010-) during which a basic conceptual design of the LC TPC is worked out.

LC TPC R&D and Beam Tests in 2010-2012

In the design phase of 2010-2012, beside the overall design of the LC TPC features two major hardware R&D issues; (a) a design of a TPC end-plate of the thickness of 15% radiation length or less, and (b) a choice of the ion gating device. A study of a light mechanical structure of the TPC end-plates has been started as well as the so-called advanced end-plate TPC modules with power pulsing and an efficient cooling such as the two-phase CO2 cooling [START_REF] Verlaat | CO2 Cooling Developments for HEP Detectors, Talk given at VERTEX[END_REF]. The plan is to build a new LP1 end-plate structure mounted with the advanced TPC modules with S-ALTRO (and also modules of the digital TPC), and test it in a beam test for the ILD-DBD (Detail Baseline Design) in 2012. This R&D phase is not yet a fully funded. In 2011, the magnet PCMAG will be modified in order to make it a superconducting magnet without liquid He supply. The modification will take about 6 months.

Test beam before 2012 and the ILC beam structure

In the current prospect of the R&D budget and support, and in the situation where the availability of a higher energy hadron test beam in 2011 seems to be not very clear, it is planned that the TPC LP with PCMAG stays at the T24-1 beam line at DESY until to the end of 2012. Optionally, small scale beam tests at high-energy hadron test beams and in a higher magnetic field using small prototypes will be organised on short notice.

At the DESY test beam, there is no plan to simulate the ILC beam bunch structure. The power pulsing of the advanced TPC modules will be tested with the beam without the ILC bunch structure. The opinion of the collaboration is that a beam to test the power pulsing is not really needed. The functional test of the power switching of the advanced TPC modules in a higher magnetic field will be necessary. To demonstrate how the ion gating device works, a proper device is required, either a laser or a flash lamp, to simulate beam backgrounds at ILC according to the beam bunch structure.

Data acquisition

In general, for a given ILC sub-detector, a dedicated data acquisition (DAQ) system is developed to suit its needs, depending on a multitude of technical issues such as data rates, number of channels to read out, etc. The DAQ system consists of the hardware-various electronics boards using various standards to get the data from the detector head to a PC-and software to control the flow of data from the detector and commands to the detector. The requirements can then lead to a DAQ system which is conceptually new or is strongly based on an existing system in use for another detector; both of which are reasonable approaches. This therefore results in very different systems when developed in isolation as is the case for several of the ILC sub-detectors; a brief review of some of the systems is given below.

Were sub-detectors to continue in isolation a programme of verification in a beam-test, then bespoke development is a sensible approach. However, should any sub-detectors wish to have combined beam-tests with another sub-detector, then more thought and planning is needed. Therefore any issues with regard to DAQ systems depend crucially on whether combined beam-tests of several sub-detectors will happen. Alternatively, given extra resources such as those provided by the AIDA project, a common approach to DAQ systems can be pursued now such that a final system for a final ILC detector will be easier to manage and integrate when it becomes a reality. Careful planning now could lead to significant benefits, with reduced risk, in the future. As a DAQ system serves a given sub-detector or detector, it is not a driver for individual or common beam tests which is dictated by the detectors themselves. As a separate goal, more generic aspects of DAQ system can be developed for future sub-detector use which will save on effort in the long-run.

Example DAQ systems CALICE DAQ

Most of the focus for the new CALICE DAQ system has been on the hardware development and firmware to control it [START_REF] Wing | Calorimeter DAQ status[END_REF][START_REF] Decotigny | CALICE DAQ & testbeams : status and perspectives[END_REF]. The system consists of several layers of concentrator cards to get the data from the detector head to a PC and storage. Given that the CALICE programme includes several different types of calorimeter, the first layer of electronics needs to convert the sub-detector-specific data into a generic structure which is then passed to the next layer. As such, the hardware system needs to be suitably generic and could in principle be used for various sub-detectors and not just calorimeters. The DAQ and slow control software are less advanced. Initially the approach was to use existing software designed to cope with large-scale systems; the programmes DOOCS [33] and XDAQ [34] have been used so far. In light of possible combined beam-tests, a survey of available software is being performed.

EUDAQ system for vertex and tracking detectors

A DAQ system developed to read out the EUDET [8] pixel telescope has been developed [START_REF] Haas | The EUDET Pixel Telescope Data Acquisition System[END_REF][START_REF] Haas | The EUDAQ Data Acquisition for the JRA1 Pixel Telescope[END_REF]. The telescope is a relatively small-scale detector and is read out via a VME-based hardware system. Major effort has been invested in writing a flexible DAQ software framework, called EUDAQ, which has been successfully used for the pixel telescope in numerous beam tests. The code is written in C++, is freely available and was fully developed by the main authors. The software has been used by several other groups when performing beam tests in conjunction with the pixel telescope. Indeed the LC-TPC collaboration are using it for their work on a TPC sub-detector [START_REF] Killenberg | DAQ for LC-TPC[END_REF]. Any new sub-detector just needs to write a producer and the EUDAQ authors should be able to integrate on the time-scale of a few days.

Towards a common DAQ system

As sub-detectors will at some point be used together, say as a complete detector slice-test, the data will have to be merged at some point. The extremes are : to develop one data acquisition system, both hardware and software, which is able to read out all sub-detectors; or for subdetector DAQ systems to all be developed in parallel and data merged at the final opportunity when it is stored. The former is unlikely given the various logistical problems whilst the latter is undesirable, potentially leading to wasted effort and a lack of coherency in the final data samples. The reality will lie somewhere in between with some common hardware used and even more so, common software. From the examples given above, the CALICE hardware could in principle be used for other sub-detectors, although this would have significant costs associated to it. The EUDAQ software may be a viable solution for CALICE calorimeters, although this needs to be demonstrated given its current use for a much smaller system. As DAQ systems for all sub-detectors are relatively well advanced, adapting to common solutions will require extra effort and will require e.g. the recent funding of AIDA to make it possible.

Taking a middle ground on common aspects of a DAQ system, some of the questions and issues which need to be addressed are listed below. These should be addressed in the AIDA project.

Common hardware

Although the hardware used for the CALICE calorimeters and the CAPTAN [START_REF] Rivera | CAPTAN : Compact and programmable data acquisition node[END_REF] project are relatively generic and could be used for other sub-detectors, it is unlikely that such an approach is possible. However, there are various common items amongst the various sub-detector groups which could be used :

Hardware which provides a trigger or a clock such as the Trigger Logic Unit [START_REF] Haas | The EUDET Pixel Telescope Data Acquisition System[END_REF] or Clock and Control Card [START_REF] Wing | Calorimeter DAQ status[END_REF] developed for the pixel telescope and CALICE calorimeters, respectively, could be used by all sub-detectors. These would uniquely identify each trigger.

A proposed "Beam Interface Card" [START_REF] Decotigny | CALICE DAQ & testbeams : status and perspectives[END_REF] could be used to monitor beam conditions taking data from e.g. scintillators, hodoscopes, etc. Its exact form is to be designed.

Common software

There are a multitude of DAQ software frameworks developed for previous or existing experiments. A critical review of these needs to be done :

Large software frameworks such as XDAQ, DOOCS, TANGO [38], etc. have been developed with large-scale, diverse apparatus in mind. Presumably they then have the necessary functionality and flexibility to provide the framework for the ILC sub-detectors. This needs investigation and the various software compared;

The EUDAQ software has been shown to work successfully with a number of different sub-detectors. However, its efficacy for reading out large systems such as the CALICE calorimeters, with thousands of channels, must be verified;

Information needed to decide on the nature of the read-out path is the data volume, zero suppression, compression, data format etc.;

It is generally agreed that all data should be converted into the common ILC offline software format, currently LCIO.

In summary, commonality between the DAQ systems of the various sub-detectors should be sought at an early stage so as to ease integration later. Given the funding of the AIDA project, this will give support to this effort in which a critical review of current DAQ hardware and software is carried out leading to a more coherent framework for future ILC detector beam tests.

Software

Software development for ILC test beam experiments has a large potential for collaboration, as typical computing tasks in high energy physics event data processing have a high degree of similarity from experiment to experiment. For example every experiment needs a way to store and retrieve the conditions data, defining the experimental setup at the time of data taking. In order to avoid duplication of effort, most of the current test beam collaborations are already using a common set of core software tools. This desirable development has been greatly fostered by the EUDET [8] project during which already existing software tools have been improved and combined into a common framework, referred to as ILCSoft [START_REF] Gaede | A Software Framework for ILC detector R&D[END_REF]. The same software framework is also used by the ILD detector concept, the CLIC detector working group and in parts by the SID detector concept. These groups work on the development and optimisation of the global detector concepts, based on Monte Carlo simulations and results from the R&D test beams. Having a joint software framework thus provides synergies for both communities, as code and knowledge can be shared easily and provide for the necessary feedback of realism into the full simulation.

ILCSoft tools

ILCSoft is based on LCIO [START_REF] Gaede | LCIO: A persistency framework for linear collider simulation studies[END_REF], which is a persistency file format for ILC studies and defines a hierarchical event data model for full detector simulation and dedicated raw data classes for beam test experiments. The core of the ILCSoft framework is defined by Marlin, a modular C++ application framework that uses LCIO as its transient and persistent event data model. Marlin is complemented by a number of software tools: GEAR which provides the high level view other detector geometry and materials as needed during reconstruction and analysis, LCCD a conditions data toolkit that provides access to the conditions data and CED a fast 3D event display. The simulation of the detector response is performed in the GEANT4 application Mokka [START_REF] Mora De Freitas | Detector simulation with MOKKA GEANT4: Present and future, Prepared for LCWS 2002[END_REF]. The geometry description in Mokka is interfaced to GEAR for reconstruction and analysis. Fig. 1 shows an overview of the main tools used in ILCSoft. The core framework is completed through a number of auxiliary tools, such as RAIDA for histograming and the utility package MarlinUtil and depends on a small set of external packages like ROOT, GSL and CLHEP. The following planned developments and improvements for LCIO are currently ongoing: Direct access to events; Splitting of events and partial reading of event data; Streaming of user defined classes which is particular useful during the development phase of a detector.

Using ROOT I/O for the implementation of these new features is under investigation. Another area of possible improvement is the geometrical description of the detector. While the current system ensures one leading source of the geometry, the Mokka simulation, it could be made more flexible by having a standalone tool that feeds into simulation, reconstruction and event displays. The development of such a flexible system is foreseen in the proposed AIDA project. This would also include mis-alignment and integration with conditions data as the distinction between geometry and conditions data is not always perfectly well defined.

CALICE and LC-TPC software

The CALICE collaboration was the first test beam group to adopt the ILCSoft framework. CALICE has been using the complete framework for their past data taking campaigns and provided very useful feedback that led to the improvement of the software tools in particular in the context of the EUDET project. CALICE is not using LCIO as their raw data format, but are converting their data to LCIO within hours of the data acquisition. This 'duplication' of raw data has proved to be less than optimal and having one raw data format only would be desirable for future beam tests [43]. Also LC-TPC was an early user of the common core software tools. They are currently working on completion of their reconstruction and analysis package MarlinTPC [START_REF] Killenberg | TPC Testbeam Software[END_REF]. In that process they improved the geometry description of the TPC in GEAR in order to meet the requirements. An example for the fruitful interplay between core software group and users. LC-TPC also suggested improvements for LCCD, namely to store the conditions data in data base tables, that can be queried using MySQL tools.

Grid computing

Large computing resources for high energy physics data processing will be available only on the Grid. All the test beam data that has been accumulated so far is stored on Grid storage elements and major Grid sites did provide so far sufficient computing resources for their analysis. This was partly facilitated due to the delay of the LHC, for which massive resources had been allocated. With the LHC now running it is important to make the Grid sites aware of the computing needs of upcoming ILC beam tests so that they can plan accordingly.

Remote control and communication tools

Besides data analysis software for beam tests, control and communication tools are an important aspect that can foster collaboration and reduce travel expenses. A nice example is the CALICE control room that was recently set up at DESY [START_REF] Karstensen | Communication Tools[END_REF] and is fully functional from the start. This room was realised for comparatively small budget, that paid off in a short period of time through savings in travel cost. With improvements in audio and video technologies, increased band widths and lower cost, modern communication tools and remote control centres will become more widespread and are likely to change the way experiments are run.

Sites

CERN

CERN offers a broad range of test beam facilities with beams originating both from the Proton Synchrotron (PS) and Super Proton Synchrotron (SPS) accelerators. At the CERN PS East Hall, there are two beam lines, T9 and T10, delivering hadrons, electrons and muons of up to 15 GeV/c and 7 GeV/c momentum respectively. During a spill length of 400 ms, occurring typically every 33 s, up to 106 particles can be delivered. Recent studies have indicated that an ILC-like beam structure can be produced at the PS. In the SPS North Area hall EHN1 there are four beam lines (H2, H4, H6, H8) with several experimental areas each. The H2, H4 and H8 lines can provide secondary hadrons, electrons or muons of up to 400 GeV/c or primary protons of up to 450 GeV/c. The H6 line has a maximum momentum of 205 GeV/c. Up to 2 × 10 8 particles per spill can be delivered. Spill lengths vary from 4.8 to 9.6 s, while spills are repeated every 14 to 48 s, depending on the number of SPS users. Together with the beams themselves, CERN provides some adjacent infrastructures, such as basic beam instrumentation. These comprise beam spectrometers for precise momentum definition, wire chambers to measure beam profiles, as well as threshold Čerenkov counters and Cedar counters for particle ID. On request a scanning table can be provided and some beam lines are equipped with magnets, which can surround the equipment under test. In 2010 the PS and SPS are scheduled to provide 28 weeks of beam. Since many years, the CERN test beams have been used extensively by the linear collider detector community. This tradition continues. In 2010 a total of 28 days are scheduled for linear collider-related tests at the PS T9 beam, 34 days at the SPS H4 beam and 48 days at the SPS H6 beam. The linear collider users represent several CALICE HCAL technology tests, SiLC tests and various vertex technology tests. For the following years, the PS and SPS test beam schedules are expected to have some dependency on the LHC schedule, with most likely a similar availability of test beams in 2011 and potentially a somewhat shorter duration in 2012. Users have two ways to apply for beam time. For short beam tests, < 2 weeks at the PS or < 1 week at the SPS, requests are addressed directly to the SP/SPS coordinator (sps.coordinator@cern.ch) by submitting a form. These requests are normally collected towards the end of the year for the following year. For beam tests of longer duration a formal request has to be addressed to the SPSC committee. Some user groups have semi-permanent beam test installations. Examples are the CMS experiment in the H2 line, the ATLAS experiment in the H8 line and the RD51 collaboration in the H4 line. Following approval by the SPSC, these installations have been built up through a common effort by the collaborations involved. What concerns the linear collider activities, the establishment of semi-permanent ILC beam line at CERN, should be requested latest by mid-2010 in order to have it available by middle of 2011.

DESY

DESY provides three electron beam lines with an energy range from 1 to 6 GeV. The beams are produced at the DESYII synchrotron which mainly serves as injector for the DORIS and PETRA accelerators and has typical up-times of 10-11 months per year. The high availability and flexible scheduling -related to intensive in-house use -are major assets of these facilities. The beam is delivered in short 30 ps bunches every 160 or 320 ms, with typical event rates of 1 kHz. All beam lines are equipped with pre-installed cables, fast networking and installations for pre-mixed gases. Moving stages, gases magnets and beam telescopes can be provided upon request, while users in general bring their own DAQ and trigger hardware. In the previous years, the infrastructure has been considerably enhanced in the framework of the EUDET initiative. The refurbished are T21 hosts the EUDET pixel telescope, while the upgraded ZEUS telescope serves users in T22. The super-conducting PC magnet provides a field of 1 T in a bore of 0.85 m. With no iron yoke, its thickness corresponds to 0.2% X 0 only. It is presently installed in T24 and heavily used for TPC R&D (see Section 3.3). Following an exceptionally extended winter shutdown, the machine is running since march 2010 throughout 2010 and is expected to have high availability also in the forthcoming years. Users can apply for beam time through the DESY test beam co-ordinators. More information is available under testbeam.desy.de.

Further European sites

The IHEP at Protvino in Russia provides electron beams between 1 and 45 GeV as well as hadron beams in this energy range. The site is available for two months in winter time. The beam test facility at Dubna, Russia, provides neutron beams with a good yield. It remains to be discussed how these facilities can be incorporated into the beam test program for linear collider detectors.

Other sites offering beam test facilities in Europe. These are PSI Villingen (CH), GSI Darmstadt (D), the ELSA beam at Bonn (D) as well as the FZD at Dresden-Rossendorf (D). Some of these were used in the past or will be used in upcoming beam test campaigns.

FNAL

Crucial to many detector development projects is the ability to test real life operations of the device in a high energy particle beam. Only a few such facilities exist in the world. The United States' only high energy detector test beam facility is the one at Fermilab. The Meson Test Beam Facility (MTest) gives users from around the world an opportunity to test the performance of their particle detectors in a variety of particle beams. A plan view of the facility is shown in Figure 2. The web site for the MTest facility can be found at http://www-ppd.fnal.gov/MTBF-w/.

Details of the beam

The test beam originates from the resonant extraction of at least one Booster batch inside the Main Injector (MI). This batch usually consists of 10-60 RF 'buckets', with buckets separated by 19 ns. Thus the batch is anywhere from 0.2-1.2 µs long. The batch is accelerated to 120 GeV, circulates around the MI, and is slowly extracted over a macroscopic slow spill using a resonant quadrupole called QXR. The full circumference of the MI is about 11 microseconds, giving a large gap between extractions. The length and duty cycle of the spill is determined by the Accelerator Division (AD), with guidance from the Office of Program Planning. For most operations there is a single 4 second long spill per minute, for a maximum of 14 hours per day. The AD has setup a procedure for easily changing from this 4 second spill to a 1 second spill. This shorter spill can then be delivered more frequently for commissioning purposes and for those groups who are data-acquisition buffer limited. The AD has also commissioned a "pinged" beam operation where beam is extracted using a pulsed operation of the QXR, with up to 4 pings per spill, each with a tunable width from 1 to 5 ms. The 120 GeV proton beam has an approximate 0.3% momentum spread and can be focused to a 7 mm RMS spot size in the user area. In addition to delivering primary protons, there are two targets on movable stages that can act as secondary beam production areas. The magnets downstream of those targets can then be tuned to deliver any secondary momentum from 0.5 GeV/c to 60 GeV/c. The momentum spread of these secondary beams depends on the energy and the details of the collimation and can range between 1-10%, with the poorer resolution beam occurring for the lower momenta. The physical size of the beam is approximately 2-5 cm rms for the lower momenta. The Table 5 shows the rate of beam delivered to the user area for some selected momenta. As part of the improvement in extending momentum range of the beam line, the MINERVA experiment (T977) proposed to install an entire new tertiary beam line in the user facility so that it can deliver 300 MeV/c pions onto their test apparatus. This beam line was begun in the US FY2008 and has recently been completed. After the completion of the MINERVA tests, this beam line will be available for other users. The target and collimator can be rolled quickly aside so that the facility can operate normally.from them as well.

Beam energy/GeV

The future of test beam at Fermilab

The Meson Test Beam Facility will be in operation for the foreseeable future, since it has demonstrated a wide variety of modes of operation. Because the facility is in heavy use, it is likely that additions and upgrades to the equipment at MTest will be incremental, with no large update at any given time. In addition to the Meson Test beam line, Fermilab will be starting a new test beam facility in the Meson Center beam line. This facility will be known as the Meson Center Test Facility, or MCenter, and will be used as an adjunct to the MTest facility. The two beam lines are virtually identical, while the user areas are complementary. While the MTest facility has a large variety of user installation areas, and a crane to support them, the MCenter facility is tighter, but has two spectrometer magnets that could be used for a variety of calorimetry studies. Currently the MIPP experiment's apparatus occupies the downstream location in MCenter. This apparatus could be used to perform tagged neutron studies, as well as support tracking for more advanced installations. With the help of a thin target a "jetty" environment could be mimicked for future beam tests. Fermilab has begun efforts to provide for a user facility in MCenter to support detector R&D. With a very successful MTest beam line, and a second MCenter beam line to augment it, then Fermilab's test beam facilities will remain in the forefront of detector support in the United States for quite time.

SLAC

End Station Test Beam (ESTB) is a approved and funded SLAC project to use a small fraction of the 13.6 GeV electron beam from the Linac Coherent Light Source (LCLS) to restore beam test capabilities in End Station A (ESA), as shown in the schematic diagram in Figure 3. Four new kicker magnets will be installed in the Beam Switch Yard (BSY) to divert 5 Hz of LCLS beam to the A-line. This beam can be transported all the way to ESA for beam instrumentation and accelerator physics studies at full electron beam intensity. Alternatively, it can be directed against a thin screen in the A-line, to produce secondary electrons or positrons with energies up to the incident energy, and a wide range of intensities including single particles per pulse suitable for detector studies. The installation of a secondary hadron target and a hadron beam line in ESA is a possible upgrade for 2011. This beam will produce pions and kaons over a broad range of momenta, suitable for particle physics and astrophysics detector development or calibration in ESA. Besides the four new kicker magnets, a new Personnel Protection System (PPS) and a new beam dump in the ESA East wall need to be installed. For the hadron target a new beam line with bend and quadrupole magnets and acceptance collimator needs to be designed and installed. The ESTB is a unique resource in all of High Energy Physics for studies requiring high energy, high intensity, low emittance electron beams in a large experimental area. These studies include accelerator instrumentation, linear collider accelerator and machine-detector interface (MDI) R&D, development of radiationhard detectors, material damage studies, and astroparticle detector research. As summarised in Table 6, ESTB also provides moderate energy (E=13.6 GeV) secondary beams of electrons and hadrons for detector R&D. Electron beams of exceptional purity, momentum definition, and small size can be delivered. The time structure of the test beams is that of the SLAC linac, and is unique in delivering picosecond pulses at known times. This makes triggering and data collection very convenient at ESTB. A tagged photon beam could also be provided. At a later stage pions are available up to about 12 GeV/c at an intensity of 1 particle/pulse, and kaons at a 1/10 of the pion rate. ESTB utilises the existing ESA, a large experimental hall 60 meters in length with 15 and 50-ton overhead cranes and excellent availability of utilities, cable plant, and components for mounting experiments. ESA is ideal for detector development and testing large scale prototypes or complete systems with high energy particles. Figure 4 shows the secondary particle yield per LCLS beam intensity in nC as a function of secondary particle energy. Funding for the four kicker magnets, new beam dump and a new PPS system is available in early 2010. We have already started with designs. The biggest task is the new PPS for ESA, where we expect the completion in early 2011, after which operation can commence. Funding for the hadron beam line is expected through 2011.

Parameters

Asian facilities

There are several low energy beam test facilities in Asia, where test of small units can be performed.

J-PARC

The 50 GeV proton synchrotron started its operation at 30 GeV in 2009. In the hadron physics facility, there are several beam lines. The K1.1 beam line will be available in 2010, where hadrons with momentum 0.5∼1.1 GeV/c and good enough particle yields are available . This beam line can be used for beam test experiments until preparation of the main experiment at K1.1 is started. The K1.8BR beam line is dedicated to the beam test experiments, and hadrons with momentum 0.5∼1.5 GeV/c are available. This beam line also will be ready in 2010. However, the particle yields are expected to be very low at the beginning to be used for the experiments. until the intensity of the proton synchrotron becomes close to the design value (100 MW).

KEK

FTBL (Fuji Test Beam Line) utilises synchrotron photons radiated from KEKB electron beam to make electron beams with momentum 0.4∼3.4 GeV/c. FTBL has been used for many beam test experiments, including ILC activities, since FTBL started its operation in 2007. FTBL is not currently available because of the shutdown (2010∼2012) for the upgrade of KEKB. ATF (Accelerator Test Facility) for the ILC can be in principle used for beam test activities. The electron beam with momentum 1.4 GeV/c has a bunch structure (2.8 ns). and the particle yield is 10 10 /s.

IHEP, Beijing

BTF (Beijing Testbeam Facility) provides primary electron beam with momentum 1.1∼1.5 GeV/c and secondary beams with momentum 0.4∼1.2 GeV/c. BTF is now under a long shut down (2008-2010) for its upgrade.

Tohoku University

The Research center for electron photon science at Tohoku University in Japan has a beam test facility providing electrons with momentum 300 MeV/c and 1.2 GeV/c. The availability of the facility is very high.

Semi-Permanent beam lines and combined beam tests

The establishment of beam lines mainly dedicated to linear collider detector R&D, called semipermanent beam lines hereafter, has been an important topic at the workshop. In general it is felt that the establishment of those beam lines would lead to important synergies. This leads from practical issues like "knowing where the trigger counters are" to the possibility to install infrastructural components like communication services at the beam test sites. The main advantages of permanent beam lines are listed in the following:

The use of a semi-permanent beam line would allow the sharing of experience with the usage of a beam line. Hence, the data taking can be much more efficient as the sometimes tedious period of getting up and running can be much shorter;

The existence of a semi-permanent beam line would foster the development of common DAQ interfaces which after all would also facilitate the data taking a lot. This can go as far that manning of shifts can be shared by different detector types, simply because the interfaces to the detectors are familiar. This in turn safes travel money and man power.

Clearly, it has to be made sure that in particular young students can still be trained at beam test sites;

A semi-permanent beam line would facilitate a situation in which one subsystem is the main user while another one acts as a secondary user to e.g. take calibration data or for long term studies. A general familiarity with a given beam line would render such a configuration much easier and allows for flexible switches between detector components if circumstances demand it;

A common remote control system may allow for data taking even if no expert of a sub-system is on-site. Clearly, this has to comply with safety aspects at the beam test sites;

A semi-permanent beam line would naturally lead to a mutual better understanding of other detector components. The fact that a common DAQ system at an early stage may facilitate the system integration in the real detector is also not to be underestimated.

In order to underline the need of semi-permanent beam lines, beam requests could be transmitted to sites in a coordinated way by the spokespersons of the detector R&D collaborations at given dates in a year. By that, several requests from the community arrive at the same time which may naturally lead to an assignment of only a few beam lines to the requests. The placing of the requests to the sites will be preceded by a brief meeting of the spokespersons in order to have an idea of schedules which could then also be streamlined. The step to a common request is not that long in that case. A short meeting on coming beam test activities will become a standing item at each linear collider workshop.

All beam test efforts will be monitored by a light monitoring system. In practise, this will be a simple date base where the groups enter the date and the purpose of the test as well as the beam line they use. This is a simple mean to facilitate communication beyond different detector system. It is very light weight and easy to implement at any computing centre (FNAL, DESY, CERN, CC IN2P3). The data base can be brought in operation during the summer/autumn of 2010.

Another question is whether the community should plan for combined beam tests, i.e. combining different detector technologies. The workshop could not identify a clear project of a major combined beam test for the period 2010-2013. There are, however, occasions at which a combination at a smaller level seems to be feasible. Calorimeters for example need very often a good point resolution. This requirement is very much met by the EUDET Telescope. It could however be imagined that such a task can be realised by a silicon tracking device conceived for linear collider detectors

Concluding remarks

This document witnesses the large amount of challenging activities in the R&D for linear collider detectors. All proposed technologies need considerable beam test resources in the coming 2-3 years. In view of the DBDs to be completed at the end of 2012, a high availability of beam test sites in the coming 2 1/2 years is of major importance. This is more important than e.g. the establishment of an ILC beam structure which on the other hand would enhance the validity of beam test results. Considerations to shutdown the beam test areas at CERN and FNAL during 2012 bear a considerable risk for all the projects. However, the sizable number of sites may allow for searching of alternatives in case a given site is not available. This document will support the coordination of the beam test activities of the linear collider detectors.

  ILC beam time structure (1ms beam + 199ms blank); Mimicking hadron jets; Common DAQ hardware and software; Common online and offline software; Common reconstruction and analysis software infrastructure; Tagged neutral hadron beams.The outcome of the IDTB07 workshop resulted in a roadmap document[START_REF] Yu Edt | World-wide ILC Detector R&D Community, Roadmap for ILC Detector R&D Test Beams[END_REF] that was released to the linear collider leadership and facility managers in summer 2007. Many of the improvements made in facilities in subsequent years were based on the requirements and the roadmap laid down in this document. Among the efforts to support the linear collider detector R&D, the following are to be highlighted: The CALICE collaboration benefited from the availability of the H6 beam test area at CERN over several months in the years 2006 and 2007. This considerable beam time was allocated on short notice, despite the huge demands required by the final stages of the LHC detector R&D program and the launch of the neutrino program at CERN. FNAL refurbished the MTest beam line particularly to host the CALICE beam test program in the years 2008 and 2009. This program is to be pursued in 2010 and beyond. The continuing availability of the test beam facility at both CERN and FNAL allowed the establishment of an infrastructure by which CALICE was able to setup remote control facilities which are a first step towards a similar detector control at a future linear collider.

Figure 1 :

 1 Figure 1: Schematic overview of the ILCSoft framework tools.

Figure 2 :

 2 Figure 2: Plan view of the Meson Test Facility at FNAL.

Figure 3 :

 3 Figure 3: End Station A Facility configuration. Primary beam experiments will be conducted along the primary beam line inside the shielded enclosure. The primary beam terminates in the beam dump shown in the ESA east wall. Secondary beam tests for detector studies will take place in an open region at the end of ESA. The proposed hadron beam line components and the new beam dump are shown in blue, overlaid onto the existing ESA setup.

Figure 4 :

 4 Figure 4: Secondary particle yields in ESA per nC of LCLS beam incident on the 0.87 r.l. Be target. The production angle is 1.50 degrees, the acceptance is 5 µsr, and the momentum bite ∆p/p = ±1%. LCLS beam energy is 13.6 GeV. For expected operating conditions, the yields at the end of ESA are roughly a factor of 4 lower.

Table 1 :

 1 Particle types: e, π, p, energies: 1-120 GeV, high rates ≈ 1 MHz for short periods The table indicate the envisaged beam test activities until the end of 2012. The acronym SU means "Test of Small Units can be expected", The acronym LS means "Large Scale Testbeam planned". Sites are given in alphabetical order. Bold face letters indicate where beam tests are going to happen. Normal face letters indicate optional tests depending on availability of detector prototypes and needs. The required strength of the magnetic field is between 3 and 6 T.

	Project	2010/2	Site	2011/1	Site	2011/2	Site	2012/1	Site	2012/2	Site
	Calo	LS	CERN	LS	CERN	LS	CERN	LS	CERN	LS	CERN
			FNAL		FNAL		FNAL		FNAL		FNAL
			SLAC		SLAC		SLAC		SLAC		SLAC
	Needs		Magnet	Magnet	Magnet	Magnet	Magnet
			Particle types: e, π, p, energies: 1-120 GeV, low rates ≈ 100 Hz
	Gas/TPC	LS		LS	CERN	LS	CERN	LS	CERN	?	CERN
			DESY		DESY		DESY		DESY		DESY
					FNAL		FNAL		FNAL		FNAL
	Needs		Magnet	Magnet	Magnet	Magnet	Magnet
			Particle types and rates: e as available at DESY, hadron beam test not planned but possible.
	SiTrack	SU	Various (see Tab.4)	SU	Various	SU	Various	SU	Various	SU	Various
	Needs	Magnet/Telescope	M./T.	M./T.	M./T.	M./T.

Table 3 :

 3 . Prototypes (ϕ and τ refer respectively to Physics and Technological CALICE prototypes), date of first test beam operations, run types & constrains, estimated time.

	Calorimeter	Date	Type	Requirements	Projected TB facility (optional)
	RPC DHCAL m 3 (ϕ)	≥ mid 2010	All types High E (in combined TB)	< 100 Hz	FNAL
	GEM DHCAL (ϕ)	≥ 2011	low E e, µ, π	-	FNAL
	µMegas, RPC layers	2009 → end 2010 low E e, µ, π		CERN
	SDHCAL m 3 (τ )	≥ end 2010	All types	< 100 Hz or ILC like	CERN (FNAL)
	W HCAL structure (ϕ) ≥ '10	All types	-	CERN
	DECAL	≥ 2011	e (all E)	Large XY table	CERN & DESY
	CALICE AHCAL (τ )	≥ 2012	e (all E), low E π	≤ 1 kHz or ILC like	CERN (FNAL)
	CALICE ECALs (τ )	≥ 2011	e (all E), low E π	≤ 1 kHz or ILC like	CERN (FNAL)
	Combined CALICE (τ ) ≥ 2011-2012	All types	≤ 0.1 -1 kHz or ILC like	CERN & FNAL
				> 3 T magnet, telescope
	SiD ECAL	≥ 2011	e 5-10+ GeV low E e, π (FNAL)	Beam localisation ILC like, low rate (0,1,2 e/Bunch) FNAL SLAC (DESY)
	SiD Muons	≥ 2011	High E had.	-	FNAL
			Combined test		FNAL
	FCAL	2010-2013	low E e	Telescope	DESY
		≥ 2012	High E electrons	Telescope	CERN
			Irradiation with e		FZD, TU Darmstadt
	DREAM	2010-2013	High E had.	-	CERN

Table 4 :

 4 Overview on the projects and beam test plans of the various groups working on Silicon Tracking and Vertex Detection. The ILC tracking and vertex detector reviews include a more comprehensive review of the efforts of the different R&D groups.

Table 5 :

 5 Rate of beam delivered to the MT6 user facility for 1 × 1011 protons in the Main Injector. Remainder of beam is identified as electrons.

		Rate at entrance	Rate at exit	% π/µ
		to MT6 (per spill) to MT6 (per spill) at exit of MT6
	16	132000	95000	82%
	8	89000	65000	42%
	4	56000	31000	26%
	2	68000	28000	< 20%
	1	69000	21000	< 10%

Table 6 :

 6 ESTB primary electron beam parameters and experimental area at the BSY and in ESA.

		BSY	ESA
	Energy/GeV	13.6	13.6
	Repetition rate/Hz	5	5
	Charge per pulse/10 10 nC	0.15-0.6 0.15-0.6
	Energy spread, σ E /E	0.058% 0.058%
	Bunch length, rms/µ	10	280
	Emittance, rms(γǫ x , γǫ y )/10 -6 mrad 1.2, 0.7	4, 1
	Spot size at waist, σ x,y /µ	-	10
	Momentum dispersion, η and η ′ /mm	-	< 10
	Driftspace available
	for experimental apparatus/m	-	60
	Driftspace available
	for experimental apparatus/m	-	5 × 5

mainly heating, mechanical integration, compactness, embedded FE electronics, power-pulsing

Acknowledgements

The linear collider detector community would like to thank the LAL directorate for giving us to opportunity to hold this workshop under optimal working conditions. We would like to thank in particular the workshop secretaries Valérie Brouillard and Patricia Chémali as well as Gérard Dreneau for the technical support. Thanks to Paul Dauncey for clarifying remarks on the status of the DECAL.

Appendix

Primary contacts for site managers: LC testbeam working group: Kiyotomo Kawagoe (Kobe University) kawagoe@kobe-u.ac.jp Jaehoon Yu (UTA) jaehoonyu@uta.edu Vaclav Vrba (FZU Prague) vrba@fzu.cz Felix Sefkow (DESY) felix.sefkow@desy.de Chair of detector R&D panel: Marcel Demarteau (FNAL) demarteau@fnal.gov Editor of this document: Roman Pöschl (LAL Orsay) poeschl@lal.in2p3.fr These persons may serve as a primary contact in case of additional questions on project plans and will establish the contact to the various groups.

References List of participants


I S Maksymov

M Besbes

J P Hugonin

J Yang

A Beveratos

I Sagnes

I Robert- Philip

P Lalanne

Metal-coated nano-cylinder cavity for broadband nonclassical light emission

A novel metal-coated nanocylinder-cavity architecture fully compatible with III-V GaInAs technology and benefiting from a broad spectral range enhancement of the localdensity-of-states is proposed as an integrated source of non-classical light. Due to a judicious selection of the mode volume, the cavity combines good collection efficiency (≈45%), large Purcell factors (≈15) over a 80-nm spectral range, and a low sensitivity to inevitable spatial mismatches between the single emitter and the cavity mode. This represents a decisive step towards the implementation of reliable solid-state devices for the generation of entangled photon pairs at infrared wavelengths.

Solid-state cavity quantum electrodynamics offers a robust and scalable platform for quantum optics experiments and the development of quantum information processing devices.

Solid-state sources of quantum states of light (single photons, indistinguishable or entangled photons) based on semiconductor quantum dots (QDs) embedded in microcavities have seen rapid progress during the past decade [1][2][3]. The microcavity (e.g. a photonic-crystal (PhC) cavity or a micropillar) induces an increase of the spontaneous emission (SE) rate and a preferential funneling of the emitted photons into the cavity mode opening the possibility of a high collection efficiency of the emitted photons. It additionally permits to circumvent some of the effects of dephasing and partially restores the coherence between the emitted photons [2,4]. However, in practice, microcavities impose a spectral and spatial matching of the emitting dipole with the cavity mode, which still limits the performance of such sources.

Techniques are presently being developed to guaranty the matching, by deterministically localizing the cavity around the randomly-placed emitting dipole [5,6] or by deterministically localizing the emitting dipole [7]. Another approach consists in designing novel architectures that are naturally less sensitive to any spectral or spatial matching. Broadband and efficient single-mode-photon sources have been recently demonstrated without any cavity effect, by use of PhC waveguides [8][9][10] or nanowire antennas [11,12]. While these single-quantumemitter architectures may offer high multi-photon probability suppression [10][11][12] and record collection efficiency through a microscope objective [11], the coherence of the emitted light is weak, and because the phase memory decay of most solid-state emitters is much faster than their radiative recombination lifetimes [2] quantum properties such as indistinguishability or entanglement are not achievable. In this letter, we propose a new architecture, ensuring both a high collection efficiency and a large SE-rate enhancement (thus restoring coherence), while relaxing constraints on spectral and spatial matching. This is achieved with a nanocylinder antenna, which operates in an intermediate confinement regime with a mode volume V≈0.002λ 3 . The mode volume is approximately 10-times larger than those achieved with ultrasmall plasmonic nanoantennas, such as nanogap in metallic dimers [13], relaxing the constraint on the emitting dipole position, but much smaller than those of PhC cavities.

Moreover, the high Purcell factor is achieved over a broad 80-nm spectral range, relaxing the constraint on the spectral matching. Such geometry is consequently a promising candidate for enhancing the capability of solid-state sources of quantum states of light, such as indistinguishable or entangled photons.

Figure 1(a) sketches the geometry considered in this letter, a textbook case consisting in a semiconductor GaAs cylinder of radius a and height H coated by a thin dielectric Si 3 N 4 adlayer and by a thick silver layer. The 5-nm dielectric layer is introduced for preventing nonradiative recombination at the interfaces and for increasing the bottom metallic mirror reflectance. In comparison with PhC cavities or microposts, the metallic coating offers smaller mode volumes and a suppression of off-resonant leaky modes [14], which boosts the emitting dipole-coupling with the cavity mode. The main drawback is the inevitable nonradiative decay rate induced by metallic losses. Except when otherwise specified, the emitting dipole is modeled as an in-plane on-axis unpolarized dipole J located at a distance h 2 from the top air-interface.

The design and interpretation are based on an approximate Fabry-Perot (FP) model.

We start by considering the fundamental nanocylinder mode, denoted TE C hereafter and assumed to be formed in the FP picture by the bouncing back and forth of the guided TE 11 cylinder modes [START_REF]By analogy with perfect metal cylindrical waveguides[END_REF] between the top and bottom interfaces. The amplitudes A + and A -in Fig. 1 We will operate above the TE11 mode cut-off radius of 50 nm. The second TM 01 mode possesses an antinode of the electric field on axis; it will be considered for analyzing the impact of off-axis emitting dipoles on the device performance. The Purcell factor F P , defined as the normalized SE rate into the fundamental nanocavity mode TE C , is given by [START_REF] Friedler | [END_REF]

F P = (1-|u t | 4 R t )|A + | 2 + (1-|u b | 4 R b )|A -| 2 , ( 1
)
where

R b =|r b | 2 , R t =|r t | 2 , u b =exp(ik 0 n eff h 1 ) and u t =exp(ik 0 n eff h 2 ) see Fig. 1(a), with k 0 =2π/λ, A + =A s [1+r b u b 2 ]/[1-r t r b (u b u t ) 2 ] and A -=A s [1+r t u t 2 ]/[1-r t r b (u b u t ) 2 ],
A s being a dipole-field coupling coefficient proportional to the oscillator strength. The extraction efficiency η(θ) is defined as the fraction of emitted photons that are collected above the top interface for the opening angle θ

η(θ) = T(θ)|u t | 2 |A + | 2 /P T , (2)
where P T =F P + γ is the total SE rate and γ is the decay rate into other cavity modes including the decay rate into the continuum of radiation modes of the cylinder. As will be shown later by comparing the FP predictions with fully vectorial finite-element-method (3D FEM) data, γ is negligible for on-axis dipoles. This drastically simplifies the design and can be attributed to the beneficial contribution of the metal-coating that inhibit the dipole-field coupling into the continuum of off-resonant radiation modes, a remarkable phenomenon already observed in micropillars [14] and nanowire lasers [17].

The coefficients, r t , r b and T(θ), of the TE 11 mode [Figs. 2(a) and 2(b)] are calculated with a 3D frequency fully-vectorial aperiodic-Fourier-Modal method (a-FMM) [18] for λ 0 =950 nm. The frequency-dependent refractive index of silver is taken from [START_REF] Palik | Handbook of Optical Constants of Solids[END_REF], n SiN =1.95

and n GaAs =3.45. Above cutoff, the reflectance of the bottom interface is R b ≈0.95, independently of the cylinder radius. That of the top interface, R t , rapidly varies at cutoff before slowly decreasing to reach the asymptotic value of R ∞ =(n GaAs -1) 2 /(n GaAs +1) 2 =0.3 for large radius (a→∞). It is considerably smaller than the mirror reflectance usually implemented in micropillars or PhC cavities. Nevertheless, the dipole-field coupling in the nanocavity is strengthened, due to the small modal volume, and high Purcell effects are achieved over a broad spectral range. The outcoupling efficiency T(θ) is approximately equal to 1-R t for θ=π/2. The energy loss, 1-R t -T(π/2) is due to the launching and absorption of plasmons on the top metallic interface and reaches a maximum value of 0.1 for a=100 nm (a≈λ 0 /10 is the relevant value of the radius for the antenna) and further decreases with a; it is only 0.05 for a=200 nm.

In Fig. 2(c) and 2(d), we show the dependence of F P and η with the cylinder radius a for λ 0 =950 nm. The results are obtained at resonance for a dipole source placed on the antinode of the cavity mode, implying that, as a varies, the cylinder height H and the dipole location h 2 also vary to maintain the FP resonance condition for the TE 11 mode (see the inset).

The quantitative agreement between the FP model predictions (curves) and fully-vectorial data obtained with a 3D FEM software (circles) shows that the model accurately captures the physics governing the dipole-field coupling of the nanocavity and convincingly supports our assumption that γ is negligible for on-axis dipoles. The general trends in Figs. For this combination of geometric parameters, the losses are still compensated by a strong dipole-field coupling due to a high reflectance of the top interface and to the small volume.

Figure 3 shows the spectral characteristics of the antenna for an intermediate cylinder radius, a=100 nm, which provides a good trade-off between extraction efficiencies (η=44% for θ=45 o ) and Purcell factors (F P =15). The striking feature is the broadband operation: the full-width at half-maximum of the F P spectrum in Fig. 3(a) is as large as the inhomogeneous broadening of self-assembled quantum-dot emission lines for instance and the extraction efficiency in Fig. 3(b) is virtually independent of the wavelength from 800 to 1100 nm. This spectral range is comparable to that recently reported for semiconductor nanowire antennas [11][12], but additionally, the present architecture supports a strong enhancement of the local density of states. The latter is essential for the generation of indistinguishable single photons and polarization entangled photons arising from the bi-exciton cascade of a single QD, so that photons emission occurs before any dephasing mechanisms take place [START_REF] Young | [END_REF]2,4]. In order to obtain a maximally entangled state, |Φ + >=(|HH>+|VV>)/√2, it is additionally necessary that both horizontal (H) and vertical (V) polarizations undergo the same Purcell enhancement and that both exciton and bi-exciton emissions are collected identically [21].

These requirements are automatically satisfied for on-axis dipoles due to the invariance by rotational symmetry. In practice, however, the QD is not exactly on-axis, the degeneracy is lifted, and the degree of entanglement is inevitably lowered. As will be shown later, the fidelity of entangled photons pairs, i.e. the similarity of the emitted state to the maximally entangled Bell state |Φ + >=1/√2 (|HH>+|VV>), can be accurately predicted for small misalignments (a 0 <50 nm) with an extended FP model, by considering only two cavity modes, the TE C fundamental mode and an additional TM C mode formed by the bouncing of the TM 01 cylinder modes in the nanocylinder. TM 01 is responsible for the degeneracy lift at small misalignments; it has no azimuthal electric-field component and its radial component possesses an on-axis node [START_REF]By analogy with perfect metal cylindrical waveguides[END_REF], excluding its coupling with on-axis QDs. With the a-FMM, we have calculated the modal reflectance of the TM 01 mode at the top and bottom interfaces.

Figure 4a shows the normalized SE rate of radial and orthoradial dipoles as a function of the radial misalignment a 0 . The results are obtained with the extended FP model for the selected nanohole geometry (a=100 nm, H=65 nm). We notice that, due to the coupling to the TM C mode, the recombination path of H-polarized photons (red-dotted line) possesses a Purcell factor higher than that of V-polarized photons (blue-dashed line); the H-polarized photons are facilitated with regard to the V-polarized ones, and this may lead to a nonmaximally entangled state or even to a loss of entanglement. To quantify this eventuality, we calculate the fidelity as Tr(ρΦ + ), where Tr(.) is the trace and ρ is the density matrix of the entangled photons emitted by an off-axis QD. The density matrix is estimated using the formalism in [21], under the assumption that the anisotropic spin exchange energy of the QD is negligible. The fidelity [Fig. 4(b)] is significantly higher than the threshold value of 0.85 required to violate the Bell inequalities, for off-axis displacements up to 60 nm. Furthermore, it remains larger than 90% over a remarkable range of off-axis locations, 0<a 0 <45 nm, an alignment precision largely within the capabilities of current fabrication technologies [6].

Note that the 3D FEM calculations of the total SE rate of the radial and orthoradial dipoles validate the bi-mode assumption of the FP model. SE-rate asymmetry is not the only cause of disentanglement; path distinguishability may also arise from emission into different cavity modes with different radiation diagrams Although the TM C mode gives rise to a strong Purcell effect (Fig. 4a), it is weakly affecting the far field collection, P TE ~10 3 P TM even for large misalignments. Since in addition the radiation diagrams of the TM C and TE C modes weakly overlap (Fig. 4d), the TM C contribution can be spatially filtered without diminishing the source's brightness, and we are confident that the fidelity is only limited by the path asymmetry of the Purcell effect (Fig. 4c).

In summary, we have investigated a new architecture for implementing III-V GaInAs solid-state sources of quantum states of light with large Purcell factors and with a good extraction efficiency over a remarkably large 80 nm spectral range. The proposed nanocavity is predicted to be capable of generating polarization entangled photon pairs with a high fidelity, even for QD misalignments up to 50 nm. The intermediate confinement regime (V≈0.002λ 3 ) of the investigated nanocavity completely relaxes the stringent spectral matching condition inherent to conventional PhC cavities, while keeping spatial matching at a reasonable level compatible with state-of-the-art nanofabrication facilities. This is not achievable with ultrasmall plasmonic antennas [13] and we believe that the present approach is a good compromise (see EPAPS) towards the integration of highly efficient solid-state sources of non-classical light. (same markers and colors as in Figs. 2c and2d). The efficiency drop predicted with the FEM at λ<850 nm is due to a resoannce of the TE 21 mode, near its cut-off at l=750 nm.

  Fig. 1(a) respectively represent the excitation coefficients of the upward and downward TE 11 modes [Fig. 1(b)], r t and r b are the modal reflection coefficients of the top and bottom interfaces, and T(θ) denotes the fraction of the energy carried by the TE 11 mode, which is scattered by the top interface into a cone defined by the opening angle θ. Figure 1(c) shows

  2(c) and 2(d) are understood by considering the different loss mechanisms, including absorption at the bottom and top interfaces, and absorption in the silver coating when the TE 11 mode bounces back and forth in the cylinder. With the FP model, we have analyzed their respective impacts, by artificially setting either |R b |=1, |R t |=1-T(π/2) or Im(n eff )=0. We find that absorption in the silver cladding is dominant. As a increases, this absorption decreases and this explains well why the efficiency increases with a to reach a maximum value of 1-R b for large a's. The general trend for F p is primarily explained by mode-volume considerations. However, near cutoff, the beneficial effect of the volume reduction is balanced by the sudden increase of the nanocylinder height H (due to a decrease of n eff , see Fig.1(c)) and of the concomitant loss in the silver cladding. F P reaches its maximum value for a≈58 nm and for a height of H=152 nm.

[

  photons only couple to the TE C mode, it is important to examine the asymmetry induced by the TM C mode. An important prediction of the extended FP model is that the TM 01 modal reflectance at the top interface is very large (≈0.99 at λ 0 =950 nm), even larger than the

Fig. 1 (

 1 Fig. 1 (Color online). (a) Cross-section of the metal-coated nanocylinder showing the main physical quantities involved in the FP model. (b) Top-view including the |E x | 2 field profile of the fundamental TE 11 mode, calculated for a=100 nm, e=5 nm and λ=950 nm. (c) Effective index n eff of the TE 11 mode for λ=950 nm.

Fig. 2 (

 2 Fig. 2 (Color online) Main physical quantities of the FP model as a function of the cylinder radius a for λ=950 nm and e=5 nm. (a) Reflectance of the top and bottom interfaces. (b) Outcoupling efficiency of the fundamental mode. (c) Purcell factor. The inset shows the H and h 2 that maintain the FP phase-matching resonance condition as a varies. (d) Extraction efficiency for several θIn (c) and (d), circles are obtained with the 3D FEM.

Fig. 3 (

 3 Fig. 3 (Color online) Spectral performance of the nanocavity for a=100 nm, e=5 nm, H=65 nm and [h 1 ,h 2 ]=[57,8] nm. (a) Purcell factor. (b) Extraction efficiency for several θ

Fig. 4 (

 4 Fig. 4 (Color online) Influence of the off-axis dipole location a 0 at λ=950 nm. (a) Red-dotted and blue-dashed curves: SE rate of the radial and orthoradial dipoles into the TE C mode. Thin gray-solid curve: SE rate of the radial dipole into the TM C mode. Black-solid curve: total SE rate of the radial dipole due to radiation into both the TE C and TM C modes. (b) Fidelity of entanglement (0.85 threshold is indicated). (c) Probability to collect a photon from the TE C (red-dotted) and TM C (blue-dashed) modes for θ=90 o . (d) Far-field radiation patterns of the TE C and TM C modes.

Acknowledgements

The work has been performed under the NanoEPR project of the 2006 NanoSci-ERA European program.