Aging effects in the COMPASS hybrid GEM-Micromegas pixelized detectors
arxiv(2024)
摘要
Large-size hybrid and pixelized GEM-Micromegas gaseous detectors (40x40
cm^2 active area) were developed and installed in 2014 and 2015 for the
COMPASS2 physics program which started at the same time. That program involved
in particular two full years of Drell-Yan studies using a high-intensity pion
beam on a thick polarized target. Although the detectors were placed behind a
thick absorber, they were exposed to an important flux of low energy neutrons
and photons. The detectors were designed to drastically reduce the discharge
rate, a major issue for non-resistive Micromegas in high hadron flux, by a
factor of more than 100 compared to the former ones. A hybrid solution was
chosen where a pre-amplifying GEM foil is placed 2 mm above the micromesh
electrode. A pixelized readout was also added in the center of the detector,
where the beam is going through, in order to track particles scattered at very
low angles. The combination of the hybrid structure and the pixelized central
readout allowed the detector to be operated in an environment with particle
flux above 10 MHz/cm^2 with very good detection efficiencies and spatial
resolution. The performance has remained stable since 2015 in terms of gain and
resolution, showing the interest of hybrid structures associating a GEM foil to
a Micromegas board to protect gaseous detectors against discharges and aging
effects
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