The MuCap experiment at the Paul Scherrer Institute has measured the rate ΛS of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1 %. A muon beam was stopped in a time projection chamber filled with 10-bar, ultrapure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. ΛS is determined from the difference between the µ − disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of 1.2 × 10 10 µ − decays, from which we extract the capture rate Λ S = (714.9 ± 5.4stat ± 5.1syst) s −1 and derive the proton's pseudoscalar coupling g P (q 2 0 = −0.88 m 2 µ ) = 8.06 ± 0.55.

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The international Muon Ionization Cooling Experiment (MICE), which is under construction at the Rutherford Appleton Laboratory (RAL), will demonstrate the principle of ionization cooling as a technique for the reduction of the phase-space volume occupied by a muon beam. Ionization cooling channels are required for the Neutrino Factory and the Muon Collider. MICE will evaluate in detail the performance of a single lattice cell of the Feasibility Study 2 cooling channel. The MICE Muon Beam has been constructed at the ISIS synchrotron at RAL, and in MICE Step I, it has been characterized using the MICE beam-instrumentation system. In this paper, the MICE Muon Beam and beam-line instrumentation are described. The muon rate is presented as a function of the beam loss generated by the MICE target dipping into the ISIS proton beam. For a 1 V signal from the ISIS beam-loss monitors downstream of our target we obtain a 30 KHz instantaneous muon rate, with a neglible pion contamination in the beam.

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