Development of Calorimeter Prototype Modules for the ILC Test Beam Program
MRI: Development of Calorimeter Prototype Modules for the International Linear Collider Test Beam Program
Jaehoon Yu1, Andrew Brandt1, James Brau2, Kaushik De1, Gary Drake3, Ray Frey2, José Repond3, David Strom2, David Underwood3, Arthur Wicklund3, Andrew White1 and Lei Xia3
- Department of Physics, The University of Texas at Arlington, Arlington, TX
- Department of Physics, The University of Oregon, Eugene, OR
- High Energy Physics Division, Argonne National Laboratory, Argonne, IL
1.Prior NSF Results Within the Last Five Years
Jaehoon Yu: University of Texas, Arlington.EIA-0216500 “Acquisition of High-Performance Computing and Information Storage Infrastructure at UTA,” 9/1/02–8/31/05, $950,000. UTA constructed a computing facility along with high storage capacity for collaborative and multi-disciplinary research at UTA and the University of Texas Southwestern Medical Center. Brought online in late 2003, the UTA high energy physics group has turned this facility into the first large U.S. DØ RegionalAnalysisCenter outside Fermilab. The computing power at the facility has been fully utilized since then. It produced several million DØ MC events and became one of the most significant contributors to the ATLAS Data Challenges. The complex is also used for an interdisciplinary grid computing course at UTA (CSE 6350).
Andrew Brandt: University of Texas, Arlington. PHY-0320554 “A Consortium for the Acquisition of Equipment to Complete a Proton Detector for the DØ Experimental Particle Physics Program,” 8/1/03–8/1/05, $90,209, sub-award from NorthernIllinoisUniversity. The majority of these funds have been used to complete the DØ forward proton detectors, which are currently taking data.
James Brau, Ray Frey, David Strom: University of Oregon. PHY-0071058, 9/1/00-8/31/03, $490,000, and PHY-0245109, 9/1/03-8/31/06, $510,000, “A Search for Gravitational Radiation at LIGO”. These awards support the involvement of the group in the LIGO Scientific Collaboration (LSC), primarily providing salary and support for students and post-doctoral researchers. The Oregon contributions have primarily been in the areas of instrumentation for environmental influences on LIGO, analysis of these influences, and searches for burst sources of gravitational radiation and development of associated techniques, especially where the burst sources are associated with external signals such as those from gamma-ray bursts.
2. Introduction
This document proposes a joint effort between the University of Texas at Arlington (UTA), the University of Oregon (UO), and Argonne National Laboratory (ANL) to develop and construct three prototype calorimeter modules to be used in a test beam program [1] for International Linear Collider (ILC) detector research and development. This proposal is a critical step in a linear collider detector development, as it will fund the instruments for testing of leading technologies for ILC calorimetry, and also provide invaluable results on hadronic shower development with a highly granular readout. The consortium assembled in this proposal is exceptionally qualified for this effort. The group is led by Jaehoon Yu (UTA), who is leading the worldwide Linear Collider testbeam effort, and along with Andrew White (UTA) has played a major role in developing one of the most promising digital hadron calorimeter (DHCAL) technologies (Gas Electrom Multiplier, GEM). Ray Frey (UO) is a leader of theAmerican ILC calorimetry group and is heading Si-W electromagnetic calorimetry (ECAL) development. JoséRepond (ANL) is also a leader of theAmerican ILC calorimetry working group and has been leading the development of another promising DHCAL technology (Resistive Plate Chambers, RPC). All of these groups have been receiving modest R&D funding from the DOE LCRD, ADR and other programs, and have made dramatic progress in these areas over the past two to three years. However, the next step forward will require the significant funding requested in this proposal for a prototype to be used in a test beam. To make the test beam possible, in addition to the three participating institutions, Fermi National Accelerator Laboratory, Stanford Linear Accelerator Center, University of Iowa, University of Chicago, Boston University, University of Iowa and University of Washington are contributing to this project.
The funds requested in this proposal will allow the consortium to develop and construct a 30-layer Si-W ECAL with its front-end readout and two 40-layer, m3, DHCALs with the two most promising active medium technologies along with their corresponding front-end electronics. These instruments will provide the opportunity to test three new calorimeter technologies for ILC detector design along with data on hadronic showers with an unprecedented granularity for significant improvement in algorithms and in detector simulations. Numerous graduate and undergraduate students will have opportunity to participate in frontier detector technology research and development. A large number of publications will result from the development and construction of these instruments and from the results of the subsequent beam tests.
3.Research Activities
High Energy Physics Research.Advances in High Energy Physics (HEP), which is concerned with a fundamental understanding of forces and the constituents of matter, require the ability to probe progressively smallerdistance scales. These smallscales are accessible through the study of interactions between particles at very high energies. While very high–energyparticles can be obtained from natural sources in the universe, their intensities are too small to provide the necessary precision for detailed studies.To obtain the statistical precision necessary for discoveries at high energies, particle accelerators are required. The next such machine, ILC,will collide electrons and positrons in an energy range of 500 to 1000 GeV and will operate at high luminosities.
To fully exploit the physics potential of the new accelerator, detectors capable of studying the details of the products of high-energy collisions and disentangling and deciphering complex signatures are required. The detectors must be capable of measuring jets of hadrons with excellent energy and angular resolutions, a critical requirement for the discovery and characterization of the postulated Higgs bosons and super-symmetric (SUSY) particles. Since calorimeters measure the energy of particles and provide information for particle identification, they play a crucial role in any experiment at a particle collider.
Linear Collider Research. Detectors at the International Linear Collider (ILC) are envisioned to be precision instruments that can measure Standard Model physics processes at the electroweak energy scale and discover new physics processes in that regime. In order to take full advantage of the physics potential of the ILC, the performance of the system of detector components comprising an experiment must be optimized, often in ways not explored by previous generations of collider detectors. In particular, the design of the calorimeter system consisting of electromagnetic and hadronic components demands new approaches to meet the precision required to accomplish the physics goals. As a precision instrument, the calorimeter will be used to measure jets from decays of vector bosons and heavy particles such as the top quark, Higgs boson, and SUSY particles. At the ILC, it will be essential to identify and distinguish the presence of a Z or W vector boson via their hadronic decay mode into two jets, requiring a dijet invariant mass resolution of about 3 GeV or, equivalently, a jet energy resolution of . None of the calorimeters in existing collider detectors have been able to achieve this level of precision.
Requirements of Calorimeters.In order to improve jet energy resolution to meet the necessary precision requirements, new methods and technologies must be explored. The Particle Flow Algorithm(PFA) builds on the energy flow algorithm [2] pioneered by the ALEPH experiment [3] at LEP [4] to reconstruct hadronic jets. In this algorithm, the relatively superior resolution of the tracking system is exploited by replacing the measured calorimeter cluster energies with the measured momenta of the associated charged tracks (~60% of the jet energy). The electromagnetic calorimeter is used to measure photon energy (~25% of jet energy). Both electromagnetic and hadronic calorimeters are used to measure the energy of neutral hadrons (~15% of jet energy). In order to optimally use a PFA, one must avoid double counting corrections that were necessary for the LEP–era detectors [5].This requires fine lateral and longitudinal calorimeter segmentation and a high spatial resolution tracking system to precisely identify the three different components of a hadronic jet. The optimization of the calorimeter designs for the application of PFA is critical to accomplish the physics goals of the ILC. The fine segmentation of the calorimeter requires a large number of readout channels, leading to the consideration of a simple one-bit readout for the hadronic calorimeter.
Research on the Behavior of Hadronic Showers.Development of PFAs relies heavily on Monte Carlo (MC) models. At present, a number of different hadronic shower development models [6 – 9] exist. These models differ significantly in several important aspects. Figure 1 shows a comparison of average predicted shower radii for 15different MC models of hadronic showers [10]. Differences up to 60%are seen. Presently, however, insufficient experimental data exists to distinguish between these models. To remedy this situation a large part of theplanned test beam program, whichutilizes the instrumentation constructed through the support of this proposal,will be devoted to the detailed measurement of hadronic showers, allowing for the improvement and validation of these models.
Research on New Calorimeter Technologies.The design of a precision calorimeter for the ILC detector requires the development and testing of new detector technologies. The funds from this proposal will allow for the design, development and construction of prototypes of three different calorimeter technologies:a silicon-tungsten (Si-W) ECAL[11] and hadronic calorimeters (HCAL) based on Resistive Plate Chambers (RPC) [12] and Gas Electron Multipliers (GEM) [13]. The analog ECAL will have lateral segmentation and employ novel electronics to keep the active gap size at 1 mm. The signals will be readout with high resolution. The HCALs will feature cell sizes of and will be readout with one-bit resolution (digital technique). Calorimeters featuring these technologies have never before been constructed on a large scale. Thus, these prototypes will provide the first opportunity to test these novel technologies in a beam environment. Simulation studies showed that the energy resolution for neutrons and K0 with digital readout is comparable to the results obtained with analog readout [14–16].
Senior Personnel / 20
Post-doctoral Fellows / 8
Graduate Students / 16
Undergraduate Students / 30
Research and Student Training.Given the opportunities provided by the frontier detector technology development contained in this proposal, we anticipate involving many physics and engineering undergraduate students in all phases of the three projects. We also anticipate student training for Masters and Ph.D. students in physics and engineering, through their participation in design, simulation, prototype construction, commissioning, data taking, as well as the analysis of the collected data. Table 1 summarizes the anticipated number of personnel who will be using the instrumentation developed through this project.
Sources of Support / Types of SupportInstitutions requesting support in this proposal / University of Texas at Arlington / Engineering for design, source and cosmic-ray testing of prototypes, construction manpower of GEM based HCAL and joint development of gas-calorimeter readout electronics
Argonne National Laboratory / Engineering for design, source and cosmic-ray testing of prototypes, construction manpower of RPC based HCAL and joint development of HCAL readout electronics
University of Oregon / Design and testing of prototypes, construction manpower for Si-W ECAL and readout electronics development and testing
Institutions NOT requesting support in this proposal / Fermilab / Engineering for design and joint development of gas-calorimeter front-endreadout electronics
SLAC / Engineering for design and joint development of Si-W EM calorimeter front-end and DAQ electronics
University of Iowa / High Voltage System design and testing; Gas distribution system design and testing, design and testing of partial HCAL electronics
Univ. of Chicago / Design and testing of partial HCAL electronics and beam tests
BostonUniversity / Design and testing of partial HCAL electronics and beam tests
Univ. of Washington / Design and testing of partial HCAL electronics and beam tests
Sources of Support.The funds requested in this proposal will provide material costs for development and construction of the three calorimeter prototypes. The engineering and personnel support will be provided by the institutions participating in this proposal, other contributinguniversities, and two national laboratories, Fermi National Accelerator Laboratory (FNAL) and Stanford Linear Accelerator Center (SLAC). Table 2 summarizes the sources and the types of support complimenting this proposal. Significant engineering and development manpower will be provided by the three national laboratories. The participating institutions will provide manpower for the local design effort, pre-prototype testing, assembly of the final prototype modules and commissioning of the modules at the test beam facility through funding sources outside of this proposal. The funds requested in this proposal will serve to acquire the material for development and construction of the three prototype modules and their readout systems
4. Description of Research Instrumentation and Needs
Implementingthe PFA concept requires a dense, highly segmented ECAL to measure the energy of electrons and photons and cleanly separate their energy depositions from those of hadrons. A highly segmented HCAL is also required to resolve the energy depositions due to charged hadrons from those due to neutral hadrons. The transverse segmentation necessary to carry out particle flow is on the order offor the ECAL and for HCAL [11] for a linear collider detector and for the test beam program [1]. The Moliere radius (a measure of the shower size) of the ECAL must be kept small, while energy resolution considerations for electron and photon final states requires approximately 30 longitudinal samples [17].
Considering only the energy measurement error for each particle in the PFA,the contribution to the energy resolution from charged hadrons in a hadronic jet is completely negligible,since their energies are replaced by the momenta measured in the tracking system. The contribution from photons is comparatively small since these are generally well behaved and measured. Thus the dominant contribution stems from the neutral hadrons. A single neutral hadron energy resolution leads to an intrinsic best jet energy resolution of . This resolution is further degraded due to imperfect separation of the energy deposits in the calorimeter and their incorrect assignment to charged or neutral particles. This additional ‘confusion term’ is estimated [18] to be the dominant contribution to the jet energy resolution of. This corresponds to more than a factor of two improvement over LEP II detectors [19, 20].
Since the pattern recognition element is a crucial factor for the design of ILC calorimeters, the behavior of hadronic showers must be understood in full detail. To date, measurements of hadronic showers with a fine spatial resolution have not been accomplished, hence the need for a much improved description.Thus, one ofthe primary scientific goalsof the test beam programto be achieved with the instrumentations from this proposal is to measure hadronic showers with unprecedented spatial resolution. The three calorimeter prototypesdeveloped and constructed through this proposal will be used to accomplish these goals. Since a test beam cannot produce jets, our approach will be to tune the existing simulation codes over the range of single particle energies expected in jets produced at the ILC, and then to optimize the detector designs using these validated codes.
We are proposing a radically new approach to the measurement of jet energies and jet-jet masses, using new technologies. The need to ensure reliable operation of a digital calorimeter system over an extended period at the ILC also requires that we have critical information available before the final technology selection. For these reasons we will build three prototypes, one ECAL and two DHCAL’s. The use of GEM and RPC for the DHCAL’s are new in the field of calorimetry. As such it is essential that both of these be tested to determine performance characteristics and reliability of operation, over an extended period, with respect to stability of construction, efficiency, multiple hits, material degradation, gas flow rates, temperature and humidity effects and beam exposure (C/m2). The extension from the present small prototypes to 400,000 channel systems will provide the confidence to make the final technology selection.
Silicon-Tungsten (Si-W) Analog Electromagnetic Calorimeter (UO).The requirements of a dense, highly segmented calorimeter have resulted in the choice of tungsten layers sampled by segmented silicon detectors as the leading candidate for the ECAL. The small Moliere radius of tungsten (9 mm) gives compact photon showers which are more easily separated from charged hadrons. At the same time, the interaction length for hadrons is relatively large for tungsten, providing higher longitudinal separability between photons and hadrons. Silicon detector wafers are readily segmented and provide adequate signal charge with a thin samplingmaterial [21]. The main questions for this technology are cost which will probably become reasonable inthe ILC timescale and the ability to handle large number of readout channels, which requires a sensible integration scheme.
In 2002, UO proposed a Si-W implementation detailed below provides an integration of silicon detectors with readout which is necessary for a realistic ILC detector. The design can provide the required transverse segmentation while maintaining the small tungsten Moliere radius by minimization of the readout gap (about 1 mm). The silicon layers are tiled with detectors which arethe size of a large silicon wafer (presently 15 cm diameter). Each detector consists of ~1000 individual pixels, nominally 5 mm across, which are connected to a single readout chip (ROC), which is bump–bondedonto the detector wafer, as depicted in Fig.2. The individual pixel signals are brought to the ROC by lines metallized directly on the wafer. The ROC is an ASIC [22] which provides full analog and digital signal processing for each pixel. It requires only ~10 external connections for serial digital output, power, and control. The ROC is placed in a cutout in the G10 motherboard, as indicated in Fig. 3.