Mean Lifetime Part 2: Cosmic Muons

Students learn how physicists measure the lifetime of a particle. Muon lifetimes are used as this is directly appicable to experiments with cosmic ray detectors and the Cosmic Ray e-Lab.

In the first part of the activity, students represent “muons” and calculate their “decay time” by rolling a die for each muon. The dice serve as a model to help students visualize muon decay. The students record the “decay times” and create a decay histogram (described below). They find half-life and lifetime from the plot. 

In the second part of the activity, students examine cosmic ray muon lifetime plots from the Cosmic Ray e-Lab and analyze them in much the same way, but this time defining a starting time (t = 0 is not necessarily on the plot) and identifying an approximately constant noise level above the horizontal axis. The teacher explains how muon lifetimes are measured in the detector (see Background Material below) before students examine plots from the Cosmic Ray e-Lab.