2010/06/21 by David M. Webber, Webber, David M.
Engineering · Physics and Astronomy · #Muon and positron interactions and applications #Particle physics theoretical and experimental studies #Dark Matter and Cosmic Phenomena
paper · pdf · doi:10.48550/arxiv.1006.3982
The Fermi constant, GF, describes the strength of the weak force and is determined most precisely from the mean life of the positive muon, taumu. Advances in theory have reduced the theoretical uncertainty on GF as calculated from taumu to a few tenths of a part per million (ppm). The remaining uncertainty on GF is entirely experimental, and is dominated by the uncertainty on taumu. The MuLan experiment is designed to measure the muon lifetime to part-per-million precision, a better-than twenty-fold improvement over the previous generation of experiments. In 2007, we reported an intermediate result, taumu=2.197013(24) microseconds (11 ppm), which is in excellent agreement with the previous world average. This mean life was measured using a pulsed surface muon beam stopped in a ferromagnetic target, surrounded by a symmetric scintillator detector array. Since this intermediate measurement, the detector was instrumented with waveform digitizers, the muon beam rate and beam extinction were increased, and two data sets were acquired on different targets, each containing over 1012 muon decays. These data will lead to a new determination of GF to better than a part per million.