MUON: Muon Lifetime

The basic building blocks of matter are quarks and leptons, and these fundamental fermions interact via forces mediated by gauge bosons corresponding to fundamental symmetries of the universe. The goal of this experiment is to measure the lifetime of one of these fundamental fermions: the muon. This lifetime determines the value of the Fermi Constant GF, which is the fundamental parameter describing the strength of low energy weak interactions. The mass of the W gauge boson can be calculated from GF by using the standard electroweak unified theory.

Several cosmic ray muons are stopped each minute in a large volume of scintillator. By studying the spectrum of time delays between muon entry into the scintillator and muon decay, the mean lifetime can be measured.

Victor Hess discovered cosmic rays in 1912, and Carl Anderson discovered the muon in 1936 while studying cosmic rays. The muon was an unexpected discovery, with I.I. Rabi famously asking "Who ordered that?" Anderson and Hess received the 1936 Nobel Prize in Physics.

Rough Interim Write-Up in PDF Format.

(The experiment is currently located in MP245; last write-up revision: September.)

Additional resources:

Photo of MUON Experiment Apparatus.

Muon Experiment Apparatus