New Precision Determination of g_p and G_F: the MuXperiments at PSI

Abstract

We discuss two precision experiments which will measure fundamental weak interaction parameters: MuLAN's goal is the measurement of the positive muon lifetime to 1 ppm, which will in turn determine the Fermi coupling constant G_F to 0.5 ppm precision. MuCAP is the first experiment which will unambiguously determine the induced pseudoscalar form factor of the proton, g_p. While contradictory experimental results for g_p are under discussion, firm theoretical calculations on the percent level within the framework of Chiral Perturbation Theory are now challenging the measurements. We will describe our experimental efforts and latest achievements.