8-13 August 2011
Rhode Island Convention Center
US/Eastern timezone

A New Part-Per-Million Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant

12 Aug 2011, 11:10
20m
551 A (Rhode Island Convention Center)

551 A

Rhode Island Convention Center

Parallel contribution Low Energy Searches for Physics Beyond the Standard Model Low Energy Searches for Physics Beyond the Standard Model

Speaker

Dr David Webber (University of Wisconsin-Madison)

Description

on behalf of the MuLan Collaboration The Fermi constant, G_F, describes the strength of the weak force and is determined most precisely from the mean life of the positive muon, tau_mu. Advances in theory have reduced the theoretical uncertainty on G_F as calculated from tau_mu to a few tenths of a part per million (ppm). Until recently, the remaining uncertainty on G_F was entirely experimental and dominated by the uncertainty on tau_mu. We report the MuLan collaboration's recent 1.0 ppm measurement of the positive muon lifetime. This measurement is over a factor of 15 more precise than any previous measurement, and is the most precise particle lifetime ever measured. The experiment used a time-structured low-energy muon beam and an array of plastic scintillators read-out by waveform digitizers and a fast data acquisition system to record over 2 x 10^12 muon decays. Two different in-vacuum muon-stopping targets were used in separate data-taking periods. The results from these two data-taking periods are in excellent agreement. The combined results give tau_{mu^+}(MuLan)=2196980.3(2.2) ps. This measurement of the muon lifetime gives the most precise value for the Fermi constant: G_F(MuLan) = 1.1663788 (7) x 10^-5 GeV^-2 (0.6 ppm). It is also used to extract the mu^-p singlet capture rate, which determines the proton's weak induced pseudoscalar coupling g_P.

Primary author

Dr David Webber (University of Wisconsin-Madison)

Presentation Materials