Design and operation of a cryogenic charge-integrating preamplifier for the MuSun experiment

Abstract

The central detector in the MuSun experiment is a pad-plane time projection ionization chamber that operates without gasamplification in deuterium at 31 K; it is used to measure the rate ofthe muon capture process μ−+d→n+n+νμ. Anew charge-sensitive preamplifier, operated at 140 K, has beendeveloped for this detector. It achieved a resolution of4.5 keV(D2) or 120 e− RMS with zero detector capacitance at1.1 μ s integration time in laboratory tests. In theexperimental environment, the electronic resolution is 10 keV(D2)or 250 e− RMS at a 0.5 μ s integration time. The excellentenergy resolution of this amplifier has enabled discrimination betweensignals from muon-catalyzed fusion and muon capture on chemicalimpurities, which will precisely determine systematic corrections dueto these processes. It is also expected to improve the muon trackingand determination of the stopping location.