Determining the Muon Mass in an Instructional Laboratory

TL;DR

This paper describes an educational experiment to measure the muon mass using cosmic-ray decay detection, spark chambers, and computer simulations, providing practical insights into particle physics measurement techniques.

Contribution

It introduces a novel instructional laboratory setup combining coincidence detection, spark chambers, and simulations to measure the muon mass in an educational setting.

Findings

Measured muon mass consistent with known values

Developed a simulation model for particle decay and detection

Demonstrated the feasibility of particle physics experiments in teaching environments

Abstract

An instructional laboratory experiment to measure the muon mass is described. Using coincidence-anticoincidence detection, the decay of a cosmic-ray muon into an electron (or positron) is observed in a multiplate spark chamber, and recorded with a triggered CCD detector. The energy of the charged decay-product particle is then quantified by counting the number of spark gaps $n_S$ it traverses before being stopped by the chamber's aluminum plates. By running this apparatus under computer-control for several hours, the number of product-particles $N(n_S)$ with various $n_s$-values is obtained. The muon mass is obtained by a least-squares fit, which compares the experimentally observed $N(n_S)$ with simulation values predicted for this distribution by the Fermi description of muon decay via the weak interaction. We present the results for the muon mass we have obtained and discuss the simulation we developed to account for the observed skewing of $N(n_S)$ due to the various directions the spark-producing product particles move as well as the escape of some of the higher-energy particles from the chamber.