Determining the Properties of the Weak Interaction Using a Cosmic Ray Muon Detector*

We have used a Cosmic Ray Muon Detector in our Modern Physics Lab that contains cylindrical scintillator pads, a photomultiplier tube, and a high voltage power source, connected to an external data acquisition module to determine the properties of the Weak interaction. Muons produced from cosmic rays come to Earth from outer space, that originate outside the solar system from stellar/supernovae explosions in the Milky Way galaxy, called Galactic-Cosmic-Rays(GCRs). When primary cosmic rays (nuclei of hydrogen atoms. i.e. protons) traveling through the interstellar medium hit the Earth's atmosphere, it collides with a nuclei of the atmospheric gas molecules, producing many secondary particles, including charged pions, that decays into a muon and two muon-neutrinos via the weak force. These cosmic ray muons travel about 99.8% of the speed of light, so their lifetime is time dilated, and hence can be detected on Earth using a muon detector. Using the Cosmic Ray Muon Detector, several experimental runs were conducted to determine the mean muon flux, mean muon lifetime, Fermi Coupling constant, Weak Coupling constant (g_w), strength of the Weak interaction (alpha_w), and the mass of the W and Z bosons.