Speaker
Description
Large size hybrid Micromegas gaseous detectors (40x40 cm² active area) were developed and installed in 2015, in view of the COMPASS2 physics program which started that year. That program involved in particular two years of Drell-Yan studies based on a high intensity pion beam on a thick polarized target. Although the detectors were placed behind an thick absorber, they were exposed to important flux of low energy hadrons, in particular neutrons. The detectors were designed to get a huge reduction of the discharge rate, a major issue for non-resistive Micromegas at high hadron flux, by a factor of above 100 compared to former ones, using the hybrid solution where a pre-amplifying GEM foil is placed 2 mm above the micromesh electrode. A pixelized read-out 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 read-out allowed to detect particle flux above 10 MHz/cm² with very good detection efficiencies and spatial resolution. Their performance remained stable since 2015 in term of gain and resolution, showing the interest of hybrid structures associating a GEM foil to a Micromegas board to protect gaseous detection against discharges and aging effects.
The hybrid Micromegas structure will be described, with an emphasis on the huge reduction of the discharge rate induced by this structure. Detector performance, in term of gain, detection efficiency and spatial resolution will be presented, and the evolution of these performance between 2015 and 2022 will be exposed to show the stability of the detectors along the time.
