Orateur
David Webber
(University of Illinois at Urbana-Champaign)
Description
The weak coupling constant, $G_F,$ 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 ppm. The remaining uncertainty
on $G_F$ is entirely experimental, and is dominated by the uncertainty on $\tau_\mu$.
The MuLan experiment is designed to measure the muon lifetime to a precision of 1 ppm,
a twenty-fold improvement over the previous generation of experiments.
In 2007, we reported an intermediate result, $\tau_\mu=2.197013(24)$ $\mathrm{\mu s}$ (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 $10^{12}$ muon decays. These data will lead to a
new determination of $G_F$ to better than a part per million.
Auteur principal
David Webber
(University of Illinois at Urbana-Champaign)
