Muon capture experiments in hydrogen and deuterium

We report about new muon lifetime precision experiments at PSI to measure the singlet μp capture rate ΛS to ⩽1% and the doublet μd capture rate ΛD to ⩽1.5%. The goal is to determine precisely the induced pseudoscalar coupling gP from ΛS, and the axial two-body current term L1A from ΛD. We have developed a new hydrogen time projection chamber (TPC) operating at 10 bar as active muon stop detector. It is surrounded by cylindrical wire chambers and a plastic hodoscope as electron detector. Ultra-high purity of the hydrogen gas (cZ<10−7) was accomplished by continuous gas circulation and purification. Isotopic purity cd<10−8 was achieved with a special isotope separation column. In total, ∼1.5×1010 good events were collected which are now in final analysis. Our first result from 10% of the statistics, gP=7.3±1.1, agrees well with the theory. The μd experiment is now in development. We will use a new TPC operating in deuterium gas at T∼30 K. The proposed experimental setup is presented.