Measurement of the Michel Parameters ρ with the MEGA positron spectrometer

ρ is one of the Michel Parameters in the theoretical expression for the differential decay rate of polarized muons. The MEGA collaboration has recently conducted an experiment that should improve the precision of ρ by at least a factor of 2 from its current best value, ρ = 0.7518 ± 0.0026. In this experiment, the energies of decay positions were measured. ρ can be extracted from the energy spectrum by comparing it with that of Monte Carlo simulations. The experiment was carried out with the existing MEGA positron spectrometer, which consists of 180 strips of plastic scintillator forming two hollow barrels and 8 cylindrically shaped MWPCs arranged such that seven smaller ones surround a larger central one. To understand and elminate possible sources of systematic error, 6 modes of data were taken during the run. Following a brief discussion of the experimental setup, the authors will discuss the major systematic effects and the current status of the data analysis