Session KL: Instrumentation IV: GEMs, Calorimeters & Drift Chambers

Development of GEM Tracker for the J-PARC E16 experiment

A GEM Tracker (GTR) is a micro-pattern gas detector using GEM foils for tracking charged particles. In the J-PARC E16 experiment, momenta of electrons and positrons from decays of the $\phi$ meson are measured by three layers of the GTRs whose sizes are $100 \times 100$, $200 \times 200$, and $300 \times 300 \ \mathrm{mm}^2$ in a magnetic field. In order to achieve a mass resolution of $5 \ \mathrm{MeV}/c^2$, position resolutions of $100 \ \mu \mathrm{m}$ in a bending direction by the magnetic field and $700 \ \mu \mathrm{m}$ in a direction perpendicular to the bending plane are required. Note that an incident angle of charged tracks to the GTR in the bending plane is up to 30$^{\circ}$. To cope with the inclined tracks, a new analysis method called ``timing method'' was developed. We have developed GTRs satisfying the requirements and evaluated their performance, such as a position resolution and detection efficiency, by beam tests. Incident angle dependencies of the evaluated items for all sizes of the GTRs were obtained as the test results. We are ready to start a final detector production for the GTRs. In this presentation, we report our GTRs and the achieved performance.   

Research and Development of Commercially-Manufactured Large GEM Foils

With future experiments proposing detectors that utilize very large-area GEM foils, there is a need for commercially available GEM foils. Double-mask etching techniques pose a clear limitation in the maximum size of GEM foils. In contrast, single-mask techniques developed at CERN would allow one to overcome those limitations. We report on the electrical and optical analysis, along with the gain and diameter size uniformity of 10 $\times$ 10 cm$^2$ and 30$\times$30 cm$^2$ GEM foils produced by Tech-Etch Inc. of Plymouth, MA, USA using single-mask techniques. This marks the beginning of large GEM foil production on a commercial basis. The Tech-Etch foils were found to have excellent electrical properties. The measured mean optical properties were found to reflect the desired parameters and are consistent with those measured in double-mask GEM foils, and show a consistent gain uniformity over the active area. These foils are well suited for future applications in Nuclear and Particle Physics where large-area tracking devices are needed.   

Study of space-charge dependence on IBF for GEM and Micromegas detectors

The MWPC is widely used in a Time Projection Chamber (TPC). To prevent ions created around amplification region from back drifting into the drift space, gating grid system is widely used in the TPC. However, the data taking rate is limited by the operation of the gating grid and the TPC with gating grid system cannot be suitable for the high rate experiments. Micor-Pattern Gaseous Detectors (MPGD) are the possible solutions to overcome the high rate limitations. GEM and Micromegas can absorb positive ions on its electrode or mesh and can reduce the ion backflow into the drift space. In this study, we aim to evaluate performance of ion back flow suppression of GEM and Micromegas detector as a function of space-charge density. We also did the simulation studies using Garfield$++$ to assess the reproducibility of the space-charge density dependence of the ion back flow obtained in the measurement. In this talk, we will report the overall performances (space-charge density and field dependences of the ion backflow) of GEM and micromegas detectors studied in the measurements and simulations.   

Performance Evaluation of the COBRA GEM for the Application of the TPC

Suppression of the back-drifting ions from avalanche region to drift space (IBF: Ion Backflow) is the key for a Time Projection Chamber (TPC) since IBF easily distorts the drift field. To suppress IBF, Gating Grid system is widely used for the TPC but this limits the data taking rate. Gas Electron Multiplier (GEM) has advantages in the reduction of IBF and high rate capability. By adopting GEM, it is possible to run a TPC continuously under high rate and high multiplicity conditions. Motivated by the study of IBF reduction for RICH with Thick COBRA, which has been developed by F. A. Amero et al., we developed COBRA GEMs for the application of a TPC. With a stack configuration, IBF reaches about 0.1 $\sim$ 0.5\%, which is $\times$ 5-10 better IBF than the standard GEMs. However, the measured energy resolution with COBRA is 20\% ($\sigma$) and this is much worse than the resolution with standard GEMs. Measurement of long-time stability of gain indicates that gain of COBRA varies significantly due to charging up effect. Simulation studies based on Garfield++ are performed for understanding quantitatively the reasons of worse energy resolution and instability of gain. In this presentation, we will report the simulation studies together with the measured performance of the COBRA GEM.   

Performance of the Cylindrical Drift Chamber and the Inner Plastic Scintillator in the BGOegg experiment

Properties of vector mesons, such as $\omega$ mesons, in nucleus are intensively measured to study interactions between mesons and nuclear medium. To study $\omega$ meson properties in nuclei, we search for the nuclear $\omega$ bound states in the LEPS2/BGOegg experiment at SPring-8. If a strongly bounded $\omega$ state exists and binding energy is measured, it gives a phenomenological information about interactions between $\omega$ meson and nuclei. $\omega$ meson is produced using the GeV $\gamma$ rays at SPring-8/LEPS2 beamline. The $\omega$ bound state is searched from the missing mass measurements of forward going protons. $\omega$ meson production is identified by detecting $\gamma$ and proton from $\omega$N $\to$ $N^{\ast}$ $\to$ $\gamma$p or $\omega$N $\to$ $\gamma\Delta$ $\to$ $\gamma\pi$p reaction. In the BGOegg experiment, charged particles are detected by Cylindrical Drift Chamber(CDC) and Inner Plastic Scintillators(IPS) around the target. CDC has 4 layers of stereo wires and each layer has 72 sense wires. IPS consists of 30 plastic scintillators. In this talk, the performance of CDC and IPS are described in detail.   

The performance of the Forward Drift Chamber in the BGOegg experiment

To study the hadron properties via meson photoproduction, the BGOegg experiment has started in December 2013 at the LEPS2 beamline at SPring-8. The energy of the photon beam is from 1.4 to 2.4 GeV and the present intensity is about 2.0 Mcps. The energy of the photon beam is measured by the tagging counter. Using the photon beam and a nuclear target, mesons are generated. The particles from meson decays and the recoiled particles are measured. The $\gamma$s from meson decays are measured by the BGOegg calorimeter and the charged particles are measured by the tracking counters and TOF counters. The forward drift chamber is located at 1.6 m downstream from the target to detect the charged particles in the forward direction. The effective area is 1280 mm in diameter and covers from 0 to 22 degrees in polar angle. The forward drift chamber consists of 6 planes. The orientations of wires are 0, and $\pm$ 60 degrees with respect to the vertical plane. The drift cell is in the shape of a square. The wire spacing is 8mm for all planes. The drift chamber has 480 readout channels. We will present the performance of the forward drift chamber in detail.   

Performance of Drift Chambers for E906/SeaQuest Drell--Yan Experiment at Fermilab

Naively, the parton distribution of the anti-u and anti-d quark were considered flavor symmetric. However, previous experiments showed that $\bar{u}$ and $\bar{d}$ are asymmetric. The E906/SeaQuest Collaboration at Fermilab is precisely measuring the $x$ dependence of the flavor asymmetry in the nucleon at large $x$ ($0.1 < x < 0.45$), where $x$ is Bjorken's scaling variables. This measurement is being performed using targets of proton, deuteron, carbon, iron and tungsten. The Drell--Yan process, $q \bar{q} \rightarrow \gamma^*\rightarrow l^+l^-$, is suited for this measurement, because the process always involves an antiquark. Thus SeaQuest measures the momenta of Drell--Yan muon pairs with a magnetic spectrometer. SeaQuest began a two-year data taking run in the 120 GeV proton beam in November 2013. There are four drift chambers in the SeaQuest spectrometer for tracking of muons. We have checked the performance of the drift chambers using the data. The single-plane efficiency, position resolution and rate tolerance of the drift chambers have been evaluated. The requirements of one of the drift chambers are $>95$\% of efficiency, $<400\ \mu $m of position resolution, and 1 kHz/wire/1 mm of rate tolerance. I will report on the results of the chamber performance investigations.   

Drift Chamber Construction for COMPASS-II Upgrade

COMPASS-II at CERN is preparing to make the world's first spin-dependent Drell-Yan (DY) measurement using a 190 GeV $\pi^-$ beam on a transversely polarized target. DY processes are ideally suited to probe quark distributions using an elementary interaction and no uncertainties from fragmentation. These processes will primarily originate from fusion of valence quarks, where the $\bar{u}$ quark from the pion interacts with the $u$ quark. This program provides the first ever test of the fundamental prediction that the sign of the $u$ quark Sivers function is opposite for DY and SIDIS. To enable this measurement, a new drift chamber named DC5 is being constructed at Old Dominion University based on the existing COMPASS DC4 chamber by CEA-Saclay and two recent prototypes built at the University of Illinois. DC5 is 2.88 by 2.48 meters and consists of 8 anode planes with 256 sense wires evenly spaced at a 4mm distance from the field wires. The four tilted planes each have an additional 64 sense wires to provide complete coverage in the corners of the detector, making a total of 2304 sense and 2312 field wire with respective diameters of 20 and 100 $\mu m$. This presentation will cover the details of the construction project and integration of DC5 into the COMPASS-II spectrometer.   

Forward Drift Chambers for the GlueX experiment

The GlueX experiment will search for exotic mesons produced by 9 GeV linearly polarized photon beam from the 12 GeV CEBAF machine. A hermetic solenoid-based detector system that includes tracking and calorimetry has been constructed. The Forward Drift Chamber (FDC) system consists of 24 circular planar drift chambers of $1~m$ diameter. Additional information from cathode strips, placed at both sides of the wire planes, is required to achieve efficient pattern recognition in the presence of high background rates in forward direction, resulting in 12,500 readout channels in total. The detection of relatively low energy photons by the electro-magnetic calorimeters imposes severe constraints on the amount of the material used in the FDC. Challenges in the production of this low-mass detector will be discussed. The FDC has been completed and recently installed in the bore of the solenoid magnet. Results from the tests of the whole detector system will be presented.   

Foward Calorimetry in ALICE at LHC

We present an upgrade proposal for calorimetry in the forward direction, FOCAL, to measure direct photons in $\eta = 3.3 - 5.3$ in ALICE at the Large Hadron Collider (LHC). We suggest to use an electromagnetic calorimeter based on the novel technology of silicon sensors with W absorbers for photons, together with a conventional hadron calorimeter for jet measurements and photon isolation. The current status of the FOCAL R\&D project will be presented.   

The performance study of an electromagnetic calorimeter BGOegg

It is considered that the mass of the $\eta^\prime$ meson decreases in nuclear matter due to the partial restoration of chiral symmetry. As a result of the effect, the $\eta^\prime$ mesic nucleus, the bound state of an $\eta^\prime$ meson and a nucleus, is expected to be formed. We mainly search for an $\eta^\prime$ mesic nucleus in the missing mass spectrum of forward going protons using a photon beam with energies from 1.4 to 3.0 GeV and a nuclear target. The experimental background can be reduced by tagging the $\eta$ meson generated in the $\eta^\prime$N$\to\eta$N conversion process, where the $\eta$ meson is identified by detecting 2$\gamma$ with an electromagnetic calorimeter BGOegg. The BGOegg consists of 1320 BGO crystals and covers a polar angle from 24 to 144 degrees around the target. The energy and position resolutions of the BGOegg are previously measured to be 1.3\% and 3.1mm at 1GeV, respectively. We study the performance of the BGOegg with data collected up to now from December 2013. In this talk, we will present the result of the performance study of the BGOegg calorimeter.