Muon Decay Study at NSRL

Abstract

A muon is an unstable subatomic particle, classified as a lepton according to the Standard Model. Muons are charged leptons with 1/2 spin. They were discovered by Neddermeyer and Anderson from hadronic cosmic ray showers. Figure 1 provides a visual representation of a cosmic ray shower in Earth’s atmosphere. At a height of 50 000 m in the atmosphere, a primary cosmic ray (mainly protons, helium, a heavy nucleus or a gamma ray) interacts with a gas molecule. The striking of a gas molecule creates a cosmic ray shower, where the energy of the primary particle is distributed among many secondary particles and gamma rays. With each interaction, the cosmic ray particles in the shower lose energy but distribute this energy among a higher number of particles. From the initial interaction, primarily heavy nuclei and pions are generated. Heavy nuclei will interact with gas molecules to produce protons, gamma rays, electrons and pions. The dominant decay mode of neutral pions is to two gamma rays, while charged pions decay to a muon and a neutrino (equation 1): $π^+ → µ^+$ + $\overline ν$ $_µ$; $π → µ$ $^-$ + $\overline v$ $_µ$.