Endcap Region Research Articles

A silicon vertex tracker for PHENIX

The PHENIX experiment will be upgraded with the Silicon Vertex Tracker (VTX). This new device will enhance the physics capabilities of PHENIX to explore the new hot and dense nuclear matter created in heavy ion collisions and proton spin structure in polarized proton-proton collisions. The vertex tracker will enable the direct measurement of heavy quark production by measuring the displaced vertex. We will build a four layer barrel detector, with two inner pixel sensors, two outer stripixel sensors, and mini-strip detectors at the end-cap region. This article will outline the physics capabilities of the new silicon tracker in the central region.

Gamma Background Simulation for the RPC Endcap and Barrel regions of CMS/LHC using GEANT4

We present results for the CMS-RPC sensitivity to gamma rays which were simulated with GEANT4 Monte-Carlo Code. The simulations were performed as a function of gamma energy in a range from 0.007 to 1000 MeV. In order to evaluate the γ -induced rates in the CMS muon system, the gamma spectra expected in the CMS endcap and barrel regions were taken into account. The estimated rates induced by an isotropic gamma source in the ME1, ME2, ME3, and ME4 were 138.0, 42.0, 29.0, and 28.0 Hz/cm 2 , respectively, when the GEANT4 standard electromagnetic package was used for the simulations. Whereas, the hit rates estimated for the MB1 and MB4 stations were ∼ 0.4 and 1.26 Hz/cm 2 , respectively, when the same gamma-ray source and the same GEANT4 package were employed for the simulatiom.

Development and testing of novel stripixel detectors for the silicon vertex tracker at PHENIX

As a part of the upgrades for the PHENIX detector at RHIC,a silicon vertex tracking detector is planned. This detector will consist of two pixel layers followed by two strip-pixel layers in the barrel region,an d four mini-strip layers in the endcap region. As a part of the development phase of the vertex detector, we have set up three sensor testing facilities at Brookhaven National Laboratory, at State University of New York, Stonybrook, and at University of New Mexico to characterize the preproduction sensors, and develop our testing and quality assurance plans. Preliminary results from these test are presented here.

A novel technique for the production of large area Z-coordinate readout planes for the BABAR muon system

The B A B AR detector, at the Stanford Linear Accelerator Center is a general-purpose detector for the study of e + e - interactions at the ϒ ( 4 S ) resonance. B A B AR's muon-detection system consists of two parts: a hexagonal barrel region and two planar endcap regions each containing 18 layers of iron ( ∼ 3.6 λ ) , with resistive plate chambers within the inter-iron gaps. These chambers have suffered deterioration in performance over the past few years and are being replaced by limited streamer tube chambers in the barrel. Each layer of the system consists of a set of up to 10 streamer tube modules oriented parallel to the beamline providing the azimuthal coordinate ( Φ ) and a single “ Z-plane” with strips oriented perpendicular the streamer tubes providing the coordinate ( Z ) along the beamline. The large area Z-planes (up to 12 m 2 ) are 1 mm thick and contain 96 strips that detect the induced charge from avalanches on the streamer tube wires. This paper reports on the novel construction technique of the Z-planes.

Production and quality control of the Barrel RPC chambers of the CMS experiment

Resistive Plate Chambers, working in avalanche mode, have been choosen as dedicated muon detector both in barrel and endcap region of the CMS experiment for their fast response and for their capability to be produced as tracking devices on large areas. The production of the barrel RPC chambers will be reported here with special enphasis on the quality control and on the acceptation criteria carried out during the production. Results of the tests with cosmic rays both in production and testing sites will be summerized putting in evidence the problems and the critical issues characterizing the different phases of the construction.

Status of the CMS PbWO 4 Electromagnetic Calorimeter

In the mass range of 110-150 GeV the favored process for Higgs boson detection via p-p collisions is via its decay into two photons, which demands a very high-resolution electromagnetic calorimeter. This physics goal plus the Large Hadron Calorimeter (LHC)-imposed design constraints of 25ns bunch spacing and a hostile radiation environment have led the Compact Muon Solenoid (CMS) collaboration to the choice of lead tungstate (PbWO4) crystals. Their relatively low room-temperature scintillation photon yield plus the presence of a 4T magnetic field have motivated the choice of photodetection devices providing gain amplification: Avalanche photodiodes (APD) in the central barrel region and vacuum phototriodes (VPT) in the forward endcap regions. In 2002 and 2003 significant changes were undertaken to the radiation-hard ∼95dB-dynamic-range readout electronics system, which now features 0.25μm CMOS ASICs, and which has been tested for the first time in particle beams. The CMS electromagnetic calorimeter is now in the construction phase. We review progress in the areas of crystals, barrel and endcap photodetection devices, the implementation of the readout electronics system redesign and the scintillation light loss monitoring system, as well as the status of assembly and quality control. We also present selected results from the autumn 2003 test beam program including noise performance obtained with the redesigned readout electronics, and irradiation studies demonstrating the performance of the laser monitoring system.

Resistive-plate-chamber background particles simulation studies for the endcap region of a compact muon solenoid/large hadron collider using the geometry and tracking code

We present a method to simulate the double-gap resistive plate chambers (RPC) background particles for the endcap region of a compact muon solenoid/large hadron collider using the geometry and tracking (GEANT) code. We demonstrate that the resistive plate chamber can be described using a realistic Monte Carlo simulation based on the GEANT code and analyzed with physics analysis work station (PAW) interfaces. Sensitivity calculations were performed for γ, e–, e+, and such particles in the range 0.1–100 MeV for their respective spectra. To evaluate the response of the detector in the large hadron collider (LHC) background environment, the γ, e–, and e+ energy spectra expected in the compact muon solenoid (CMS) muon endcap region were taken into account whereas the RPC sensitivity was evaluated as a function of the detector size.PACS Nos.: 7.77.Ka, 7.85.Fv

The MGPA electromagnetic calorimeter readout chip for CMS

The multiple-gain preamplifier (MGPA) is a three-gain channel 0.25 /spl mu/m CMOS chip matched to the noise and linearity requirements of the electromagnetic calorimeter for the Compact Muon Solenoid (CMS) experiment. A choice of external feedback components to the first-stage amplifier allows the chip to match the different full-scale signal and noise requirements for both barrel and end-cap regions of the detector. For the barrel (end-cap) application the noise is less than 10 000 (3,500) electrons at a peaking time of 40 ns and an integral nonlinearity of approximately /spl plusmn/0.1% full-scale is achieved for all three gain ranges. Details of the design and performance are presented, including measurements of nonlinearity, pulse-shape matching, noise, and radiation tolerance.

Vacuum phototriodes for the CMS electromagnetic calorimeter endcap

The measurement of scintillation light from the lead tungstate crystals of the Compact Muon Solenoid (CMS) electromagnetic calorimeter (ECAL) poses a substantial technical challenge, particularly in the endcap regions, where the radiation levels are highest. The photodetectors must be fast, sensitive, radiation-hard, and operate with significant internal gain in a magnetic field of 4 Tesla. The measured performance characteristics of the first batches of series production vacuum phototriodes (VPT), developed to satisfy the needs of CMS, will be described.

The cosmic ray hodoscopes for testing thin gap chambers at the Technion and Tel Aviv University

Thin gap chambers (TGCs) are built for the muon trigger chambers in the endcap region of the LHC experiment ATLAS. More than 2500 ATLAS TGCs are being produced at the Weizmann institute in Israel, and in Shandong University in China. Detailed testing of these chambers is performed at the Technion and at the Tel-Aviv University. Two cosmic ray hodoscopes for testing the operation of these detectors were built in Israel. In these hodoscopes the response of the chambers to energetic cosmic ray muons is recorded and analyzed. The hodoscopes measure the exact time and space location of the cosmic ray hit and read out the chambers which are being tested to verify that they produce a corresponding signal within the required time interval. The cosmic ray hodoscopes built at the Technion and at the Tel Aviv University for the test of ATLAS TGCs are described. The mechanical structure, readout electronics, data acquisition and operating scheme are presented. Typical TGC test results are presented and discussed.

The trigger chambers of the ATLAS muon spectrometer: production and tests

The ATLAS Muon Spectrometer (ATLAS Collaboration, ATLAS Muon Spectrometer Technical Design Report CERN/LHCC/97-22, ATLAS TDR 10, 1997.) will use dedicated detectors to trigger on muons and to identify the bunch-crossing at the appropriate rate. The Spectrometer has been designed to perform stand-alone triggering and measurement of muon transverse momentum up to 1 TeV with good resolution (from 3% up to 10% at 1 TeV). The magnetic system is composed of three large superconducting air-core toroids instrumented with trigger and high-precision tracking chambers, a central part (barrel) composed of eight coils and two end-cap magnets. The high-precision tracking system is based on Monitored Drift Tube (MDT) and Cathode Strip Chambers (CSC) in the small angle-regions. The Level-1 trigger is provided by Resistive Plate Chambers (RPC) in the barrel and Thin Gap Chambers (TGC) in the end-cap. These detectors will also measure the track coordinates in the magnetic field direction (second coordinate), to complement the precision tracking provided by the MDT which only measure the track coordinates in the bending direction of the magnetic field. The trigger system covers an area of 3650 m 2 in the barrel and 2900 m 2 in the end-cap. In the barrel region three double-gap RPC stations are used, two in the middle and one in the outer MDT chamber layer. In the end-cap region one triple-gap TGC station is used, in front of the middle MDT station, and two double-gap TGC stations behind it. The mass production of both systems is under way. The systems were involved in extensive beam tests in 2002–2003, testing their compliance with LHC timing requirements using 25 ns beam bunching to emulate the LHC beam structure, aging under critical environment conditions and so on.

Search for a high-rate gas mixture in the streamer mode operation

In Belle resistive plate chambers (RPCs), the outermost few layers of the endcap region suffer background (hit rate: 1.4Hz/cm2) due to neutrons originating from the accelerator. In the future super-KEKB, the hit rate is expected to be ten times higher. To use the present glass RPC in such environment, it is necessary to use high-rate gas in addition to the extra shielding. Gas mixtures with SF6 are promising candidates.

Characteristics of a double gap resistive plate chamber for the endcap region of CMS/LHC: data vs. simulation in avalanche mode

We present the detailed analysis of the time and charge signals of a prototype double gap resistive plate chamber for the endcap region of the compact muon solenoid detector at CERN LHC. We demonstrate that the operating high-voltage plateau can be extended at least up to 400V with the present design. The simple avalanche multiplication model can reproduce the experimental charge spectra reasonably well at the beginning of the high-voltage plateau region. The effective Townsend coefficient is estimated in the avalanche mode operation.

Techniques developed for the ATLAS thin gap chambers mass production in Japan

The thin gap chambers (TGCs) are used for the muon trigger system in the end-cap regions of the ATLAS detector. The TGC mass production phase at High Energy Accelerator Research Organization (KEK) started in January 2001. As the anode-cathode distance is small, 1.4 mm, chamber flatness is essential to achieve a uniform gas gain over the chamber. In order to perform a stable production with high quality we developed a chamber closing system. When we glue two half-chambers together, we sandwich them between a granite table and an aluminum honeycomb panel to keep the chamber flat from both sides. By using silk screens, we control the quantity of epoxy adhesive that affects the chamber thickness. Due to these developments, we can achieve the flatness of less than 100 /spl mu/m. Uniformity of detection efficiency of the TGC is measured with a cosmic-ray test bench at Kobe University. So far we have tested 300 TGCs. Position dependence of the efficiency is measured with a granularity of 5 mm /spl times/ 5 mm. The average efficiency over the tested chambers is achieved to be 99% excluding the wire supports and spacers.

Local Softness versus Local Density of States as Reactivity Index

The definition of softness and local softness using the density of states (DOS) and local density of states (LDOS) given by Yang and Parr for metals has been casted into working equations and applied to sequences of finite cylindrical fullerenes modeling the (5,5) and (10,10) single-walled capped carbon nanotubes. The behavior of DOS, LDOS, and global and local softness as functions of length and tube type is investigated in the simplest Huckel approximation. DOS-based calculation of global softness gives results that depend less on the details of the electronic structure than those based on the finite-difference approximation. Armchair single-walled nanotubes with larger diameters are softer than those with smaller diameters at the same tube length. Local softness, after fluctuations in the end-cap region, settles down within the first 20 layers of hexagons of the tube body to a constant (diameter-dependent) value.

Recent developments in crystal calorimeters (featuring the CMS PbWO 4 electromagnetic calorimeter)

In the mass range of 110–150 GeV the favored process for Higgs boson detection via p-p collisions is via its decay into two photons, which demands a very high-resolution electromagnetic calorimeter. This physics goal plus the Large Hadron Calorimeter (LHC)-imposed design constraints of 25ns bunch spacing and a hostile radiation environment have led the Compact Muon Solenoid (CMS) collaboration to the choice of lead tungstate (PbWO 4) crystals. These factors plus the presence of a 4T magnetic field and the relatively low room-temperature scintillation photon yield of PbWO 4 make photodetection a real challenge, which CMS has met via the choice of devices providing gain amplification: Avalanche photodiodes (APD) in the central barrel region and vacuum phototriodes (VPT) in the forward and backward endcap regions. In the past year the CMS electromagnetic calorimeter has entered the construction phase. We review progress in the areas of crystals, barrel and endcap photodetection devices, plans for detector calibration as well as the status of assembly and quality control. We also invoke relevant developments in other crystal calorimeters currently in operation or under development. Crystal calorimeters remain the medium of choice for precision energy and position measurements in high energy physics.

The response to high magnetic fields of the vacuum phototriodes for the Compact Muon Solenoid endcap electromagnetic calorimeter

The endcap electromagnetic calorimeter of the compact muon solenoid detects particles with the dense fast scintillator lead tungstate (PbWO4). Due to the low light yield of this scintillator, photodetectors with internal gain are required. Silicon avalanche photodiodes cannot be used in the endcap region due to the intense neutron flux. Following an extensive R&D programme, 26mm diameter single-stage photomultipliers (vacuum phototriodes) have been chosen as the photodetector in the endcap region. The first 1400 production devices are currently being evaluated following recent tests of a pre-production batch of 500 tubes. Tubes passing our acceptance tests have responses, averaged over the angular acceptance of the endcap calorimeter, corresponding to the range 20–55electrons/MeV deposited in PbWO4. These phototriodes operate, with a typical gain of 10, in magnetic fields up to 4T.

Performance of the ATLAS hadronic end-cap calorimeter in beam tests

Modules of the ATLAS liquid argon Hadronic End-cap Calorimeter (HEC) were exposed to beams of electrons, muons and pions in the energy range 6⩽E⩽200GeV at the CERN SPS. A description of the HEC and of the beam test setup are given. Results on the energy response and resolution are presented and compared with simulations. The ATLAS energy resolution for jets in the end-cap region is inferred and meets the ATLAS requirements.

The CMS muon detector

The muon detection system of the Compact Muon Solenoid experiment is described. It consists of three different detector technologies: drift tubes in the barrel region, cathode strip chambers in the endcap region and resistive plate chambers in both barrel and endcap regions. The CMS muon detection system ensures excellent muon detection and efficient triggering in the pseudorapidity range 0< η<2.4. The most recent developments and some results from the R&D program will also be discussed.

Performance of a large forward resistive plate chamber for the CMS/LHC under high radiation environment

We present the first beam test results of a real size prototype RPC for the endcap region of the CMS, one of large detectors at CERN LHC. The chamber was built with relatively low resistivity bakelite made in Korea and was operated successfully at the Gamma Irradiation Facility at CERN under the highest photon flux available, which corresponds to an effective cluster rate up to about 800 Hz/ cm 2 . The cross-talk effects between strips and sectors have been studied extensively. The high voltage plateau, which satisfies the CMS requirements for efficiency and the number of strips fired per cluster, extends to at least 300 V . The time resolution has been measured to be better than 1.3 ns in this HV plateau region. These results demonstrate that the current design of the device can be used as a muon trigger detector for the CMS forward region.