Development of a new experimental method for studies of muon capture in hydrogen

A new experiment is under preparation with the aim to improve considerably the present knowledge of the rate Lambda(s), which should be measured on a level of 1% or better, for the basic electroweak capture reaction of a negative muon on the free proton mup(1s) --> n + nu(mu). The capture rate will be determined by measuring the lifetime of mu(-) stopped in ultra pure hydrogen at 10 bar pressure and comparing it with the lifetime of the unbound mu(+). A new experimental method was developed for this project which should allow measuring the mu(-) lifetime with at least 10 ppm precision. The basic element of the detector is operating in the hydrogen gas time projection chamber (TPC) surrounded by multi-wire proportional chambers (MWPCs) and scintillator counters. The arrival times and trajectories of the incoming muons and the outgoing decay electrons are measured with this device providing effective suppression of background. Using the TPC as an active target, we can monitor on-line the protium contamination by impurities with a sensitivity better than 10(-8). This can be done by detecting the charged products of the muon capture reaction on these impurities. It was demonstrated that the TPC and MWPCs can operate in pure hydrogen under 10 bar pressure providing gas gain up to 10 000

Precise measurement of muon capture on the proton

The aim of the muCap experiment is a 1% measurement of the singlet capture rate Lambda(S) for the basic electro-weak reaction mu + p --> n + nu(mu). This observable is sensitive to the weak form-factors of the nucleon, in particular to the induced pseudoscalar coupling constant g(p). It will provide a rigorous test of theoretical predictions based on the Standard Model and effective theories of QCD. The present method is based on high precision lifetime measurements of mu(-) in hydrogen gas and the comparison with the free mu(+) lifetime. The mu(-) experiment will be performed in ultra-clean, deuterium-depleted H-2 gas at 10 bar. Low density compared to liquid H-2 is chosen to avoid uncertainties due to ppmu formation. A time projection chamber acts as a pure hydrogen active target. It defines the muon stop position in 3D and detects rare background reactions. Decay electrons are tracked in cylindrical wire-chambers and a scintillator array covering 75% of 4pi