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A new experiment is under preparation with the aim to improve considerably the present knowledge of the rate 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 µp 1s −→ n + ν µ . The capture rate will be determined by measuring the lifetime of µ − stopped in ultra pure hydrogen at 10 bar pressure and comparing it with the lifetime of the unbound µ + . A new experimental method was developed for this project which should allow measuring the µ − 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.

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