Investigation and Mitigation of Crosstalk in the Prototype ME0 GEM Detector for the Phase-2 Muon System Upgrade of the CMS Experiment: On behalf of the CMS Muon Group

The LHe is currently undergoing a high luminosity upgrade, which is set to increase the instantaneous luminosity by at least a factor of five. This luminosity increase will result in a higher muon flux rate in the forward region and overwhelm the current trigger system of the CMS experiment. The MEO, a gas electron multiplier detector, is proposed for the Phase-2 Muon System Upgrade for the CMS experiment to help increase the muon acceptance and to control the Level 1 muon trigger rate. A recent design iteration of this detector features GEM foils that are segmented on both sides, which helps to lower the probability of high voltage discharges. However, during preliminary testing of the chamber, substantial crosstalk between readout sectors was observed. Here, we investigate, characterize, and quantify the crosstalk present in the detector, and also estimate the performance of the chamber as a result of this crosstalk via simulation results of the detector dead time, efficiency loss, and frontend electronics response. The results of crosstalk via signals produced by applying a square voltage pulse directly on the readout strips of the detector with a signal generator are summarized. We also present the efficacy of mitigation strategies including bypass capacitors and increasing the area of the HV segments on the third GEM foil in the detector. We find that the crosstalk is a result of capacitive coupling between the readout strips on the readout board and between the readout strips and the bottom of the third GEM foil. Our results show that the crosstalk generally follows a pattern where the largest magnitude of crosstalk is within the same azimuthal readout segment in the detector, and in the next-nearest horizontal segments in eta. Generally, the bypass capacitors and increased area of the HV segments successfully lower the crosstalk in the sectors where they are located; on average, we observe a maximum decrease of crosstalk in sectors previously experiencing crosstalk from (1.66±0.03)% to (1.11±0.02)% with all HV segments connected in parallel on the bottom of the third GEM foil, with the addition of an HV low-pass filter connected to this electrode, and an HV divider. However, with these mitigation strategies, we also observe slightly increased crosstalk (≨ 0.4%) in readout sectors farther away.