0 41 00 42 v 2 3 1 O ct 2 00 4 Precision muon lifetime and capture experiments at PSI

a * on behalf of the µLan † and µCap ‡ Collaborations. The µLan experiment at the Paul Scherrer Institute will measure the lifetime of the positive muon with a precision of 1 ppm, giving a value for the Fermi coupling constant GF at the level of 0.5 ppm. Meanwhile, by measuring the observed lifetime of the negative muon in pure hydrogen, the µCap experiment will determine the rate of muon capture, giving the proton's pseudoscalar coupling gp to 7%. This coupling can be calculated precisely from heavy baryon chiral perturbation theory and therefore permits a test of QCD's chiral symmetry.