Study of high-pressure hydrogen-operated wire chambers designed for a precision measurement of the singlet μp capture rate

This work was carried out as part of a project aiming at a greatly improved measurement of the muon capture rate from the singlet state of the μp atom. The experiment will be performed at the intense muon beam of PSI using a new experimental method allowing high precision measurements of the lifetime of muons stopped in ultra-pure deuterium-depleted hydrogen (protium). The basic element of the detector is a time projection chamber operating in hydrogen gas at 10 bar pressure. The arrival times and trajectories of the incoming muons and the outgoing decay electrons are measured with this device providing effective suppression of background. The system of chambers and electronics is designed for the large muon stop rates required for attaining high statistical accuracy. During four beam periods at PSI, data were taken. Also, various studies of the MWPC performance in hydrogen were made including ageing studies of the chambers under irradiation with stopped muons and with alpha and beta sources. It was demonstrated that the MWPCs can operate in pure hydrogen under 10 bar pressure with gas gains up to 5000, which is sufficient for the detection of relativistic electrons.