Mulan: a part-per-million measurement of the muon lifetime and determination of the Fermi constant

The part-per-million measurement of the positive muon lifetime and determination of the Fermi constant by the MuLan experiment at the Paul Scherrer Institute is reviewed. The experiment used an innovative, time-structured, surface muon beam and a near-4\piπ, finely-segmented, plastic scintillator positron detector. Two in-vacuum muon stopping targets were used: a ferromagnetic foil with a large internal magnetic field, and a quartz crystal in a moderate external magnetic field. The experiment acquired a dataset of 1.6 \times 10^{12}1.6×1012 positive muon decays and obtained a muon lifetime \tau_{\mu} = 2\, 196\, 980.3(2.2)τμ=2196980.3(2.2)~ps (1.0~ppm) and Fermi constant G_F = 1.166\, 378\, 7(6) \times 10^{-5}F=1.1663787(6)×10−5 GeV^{-2}−2 (0.5~ppm). The thirty-fold improvement in \tau_{\mu}τμ has proven valuable for precision measurements in nuclear muon capture and the commensurate improvement in G_FF has proven valuable for precision tests of the standard model.

Development of the CsI(Tl) Muon Beam Profile Monitor for the Muon g − 2/EDM Experiment at J-PARC

In this work a muon beam profile monitor based on a thin CsI(Tl) screen with optical readout is suggested. This monitor is intended to measure an upcoming surface muon beam to the silica aerogel target of the muon g−2/EDM experiment at J-PARC. The measurements of luminophore foil parameters with a camera were done as well as the test of the monitor prototype with a surface muon beam at D2 beamline in J-PARC MLF.