Long-term efficiency analysis of GEM detectors at the COMPASS experiment

Detectors based on the Gas Electron Multiplier (GEM) are the backbone of the inner tracking system of the COMPASS experiment at CERN. They provide high position resolutions of the order of 70 μm even at very high particle rates close to the beam. The detectors have been built in 2001-2002 and have been used continuously since then. The data taken with COMPASS until now provide a unique basis to investigate the long-term performance of these detectors in high-intensity muon and hadron beams. As a first step, we investigate the 2D efficiencies of all 22 detector planes, extracted from physics runs and compare the results for different years, using data from the 2008 hadron run and from the 2015 Drell-Yan run, and discuss the observed effects.