Calibration of a Micromegas-based gaseous time projection chamber using cosmic ray muons

Abstract

We report the calibration of a gaseous Time Projection Chamber based on Micromegas charge readout modules with cosmic ray muons, utilizing their penetrating power and relatively uniform energy deposition per unit length. Muon events were selected through track reconstruction to characterize detector performances, such as the drift velocity, electron lifetime, detector gain, and electric field distortion. The evolution of detector performances over a 50-day data-taking cycle was measured with the muon calibration method. For instance, the drift velocity degraded from 3.40 ± 0.07 cm/μs to 3.06 ± 0.06 cm/μs without gas purification, and then recovered with gas purification. A 137Cs calibration source was also placed inside the detector as a reference for muon calibrations.