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Register a new userTriple GEM Detectors for the Forward Tracker in STAR
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Future measurements of the flavor-separated spin structure of the proton via parity-violating W boson production at RHIC require an upgrade of the forward tracking system of the STAR detector. This upgrade will allow the reconstruction of the charge sign of electrons and positrons produced from decaying W bosons. A design based on six large area triple GEM disks using GEM foils produced by Tech-Etch Inc. has emerged as a cost-effective solution to provide the necessary tracking precision. We report first results from a beam test of three test detectors using Tech-Etch produced GEM foils and a laser etched two dimensional strip readout. The detectors show good operational stability, high efficiency and a spacial resolution of around 70 um or better, exceeding the requirements for the forward tracking upgrade. The influence of the angle of incidence of the particles on the spatial resolution of the detectors has also been studied in detail.
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The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is in the process of designing and constructing a forward tracking system based on triple GEM technology. This upgrade is necessary to give STAR the capability to reconstruct and identify the charge sign of W bosons over an extended rapidity range through their leptonic decay mode into an electron (positron) and a neutrino. This will allow a detailed study of the flavor-separated spin structure of the proton in polarized p + p collisions uniquely available at RHIC. The Forward GEM Tracker FGT will consist of six triple GEM disks with an outer radius of ~39 cm and an inner radius of ~10.5 cm, arranged along the beam pipe, covering the pseudo-rapidity range from 1.0 to 2.0 over a wide range of collision vertices. The GEM foils will be produced by Tech-Etch, Inc. Beam tests with test detectors using 10 cm x 10 cm Tech-Etch GEM foils and a two dimensional orthogonal strip readout have demonstrated a spatial resolution of 70 um or better and high efficiency.
Triple-GEM detectors are a well known technology in high energy physics. In order to have a complete understanding of their behavior, in parallel with on beam testing, a Monte Carlo code has to be developed to simulate their response to the passage of particles. The software must take into account all the physical processes involved from the primary ionization up to the signal formation, e.g. the avalanche multiplication and the effect of the diffusion on the electrons. In the case of gas detectors, existing software such as Garfield already perform a very detailed simulation but are CPU time consuming. A description of a reliable but faster simulation is presented here: it uses a parametric description of the variables of interest obtained by suitable preliminary Garfield simulations and tuned to the test beam data. It can reproduce the real values of the charge measured by the strip, needed to reconstruct the position with the Charge Centroid method. In addition, particular attention was put to the simulation of the timing information, which permits to apply also the micro-Time Projection Chamber position reconstruction, for the first time on a triple-GEM. A comparison between simulation and experimental values of some sentinel variables in different conditions of magnetic field, high voltage settings and incident angle will be shown.
Many experiments are currently using or proposing to use large area GEM foils in their detectors, which is creating a need for commercially available GEM foils. Currently CERN is the only main distributor of large GEM foils, however with the growing interest in GEM technology keeping up with the increasing demand for GEMs will be difficult. Thus the commercialization of GEMs up to 50 $times$ 50 cm$^2$ has been established by Tech-Etch Inc. of Plymouth, MA, USA using the single-mask technique. The electrical performance and optical quality of the single-mask GEM foils have been found to be on par with those produced by CERN. The next critical step towards validating the Tech-Etch single-mask GEM foils is to test their performance under physics conditions. These measurements will allow us to quantify and compare the gain and efficiency of the detector to other triple-GEM detectors. This will be done by constructing several single-mask triple-GEM detectors, using foils manufactured by Tech-Etch, which follow the design used by the STAR Forward GEM Tracker (FGT). These detectors will investigate ways in which to further decrease the material budget and increase the efficiency of the detector by incorporating perforated Kapton spacer rings rather than G10 spacing grids to reduce the dead area of the detector. The materials and tooling needed to assemble the triple-GEM detectors have been acquired. The GEM foils have been electrically tested, and a handful have been optically scanned. We found these results to be consistent with GEM foils produced by CERN. With the success of these initial tests, construction of the triple-GEM detectors is now under way.
We present analytical calculations, Finite Element Analysis modeling, and physical measurements of the interstrip capacitances for different potential strip geometries and dimensions of the readout boards for the GE2/1 triple-Gas Electron Multiplier detector in the CMS muon system upgrade. The main goal of the study is to find configurations that minimize the interstrip capacitances and consequently maximize the signal-to-noise ratio for the detector. We find agreement at the 1.5--4.8% level between the two methods of calculations and on the average at the 17% level between calculations and measurements. A configuration with halved strip lengths and doubled strip widths results in a measured 27--29% reduction over the original configuration while leaving the total number of strips unchanged. We have now adopted this design modification for all eight module types of the GE2/1 detector and will produce the final detector with this new strip design.
We report the status of R&D on large triple-GEM detectors for a forward tracker (FT) in an experiment at a future Electron Ion Collider (EIC) that will improve our understanding of QCD. We have designed a detector prototype specifically targeted for the EIC-FT, which has a trapezoidal shape with 30.1 degrees opening angle. We are investigating different detector assembly techniques and signal readout technologies, but have designed a common GEM foil to minimize NRE cost for foil production. The assembly techniques comprise either a purely mechanical method including foil stretching as pioneered by CMS but with certain modifications, or gluing foils to frames that are then assembled mechanically, or gluing foils to frames that are then glued together. The first two assembly techniques allow for re-opening chambers so that a GEM foil can be replaced if it is damaged. For readout technologies, we are pursuing a cost-effective one-dimensional readout with wide zigzag strips that maintains reasonable spatial resolution, as well two-dimensional readouts - one with stereo-angle (u-v) strips and another with r-phi strips. In addition, we aim at an overall low-mass detector design to facilitate good energy resolution for electrons scattered at low momenta. We present design for GEM foils and other detector parts, which we plan to entirely acquire from U.S. companies.
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