Physics of fundamental Symmetries and Interactions - PSI2010

Precision measurement of the positive muon lifetime by the MuLan collaboration

12 Oct 2010, 14:30

25m

Main Auditorium (WHGA/001) (PSI)

Oral Precision experiments with pions and muons Session Tu - 3

Speaker

Prof. David Hertzog (University of Washington)

Description

The Fermi constant $G_{\mathrm{F}}$ governs the rates of all weak interaction processes and, along with the fine structure constant $\alpha$ and the $Z$-boson mass $M_Z$, it is one of the principal input parameters to the Standard Model. Owing to the purely leptonic nature of the muon decay process, $G_{\mathrm{F}}$ is extracted most precisely from measurements of the muon lifetime ${\tau }_{\mu }$. In 1999, the publication of missing radiative corrections effectively eliminated the largest, purely theoretical uncertainty in extracting $G_{\mathrm{F}}$ from ${\tau }_{\mu }$. At present, the precision in $G_{\mathrm{F}}$ is limited by experimental uncertainty in ${\tau }_{\mu }$. We report a measurement of the positive muon lifetime to a precision of one part-per-million, a better than twenty-fold improvement over the previoius generation of experiments. The new result will improve precision in $G_F$ to better than 0.8 parts-per-million. The MuLan experiment was conducted at the Paul Scherrer Institute in Villigen, Switzerland, using a pulsed surface muon beam, in-vacuum muon-stopping targets, and a large acceptance, finely segmented scintillator array. We will describe our measurement method and report our final result.

Presentation materials

Slides

PSI-MuLan-final.pdf

PSI-MuLan-final.ppt