Science, Tech, Math › Science All About the Muon Share Flipboard Email Print The green dot on the right represents the muon. MEHAU KULYK/Getty Images Science Physics Physics Laws, Concepts, and Principles Quantum Physics Important Physicists Thermodynamics Cosmology & Astrophysics Chemistry Biology Geology Astronomy Weather & Climate By Andrew Zimmerman Jones Math and Physics Expert M.S., Mathematics Education, Indiana University B.A., Physics, Wabash College Andrew Zimmerman Jones is a science writer, educator, and researcher. He is the co-author of "String Theory for Dummies." our editorial process Andrew Zimmerman Jones Updated November 08, 2017 The muon is a fundamental particle that is part of the Standard Model of particle physics. It is a type of lepton particle, similar to the electron but with a heavier mass. The mass of a muon is about 105.7 MeV/ c 2, which is about 200 times the mass of an electron. It also possesses a negative charge and a spin of 1/2. The muon is an unstable particle which exists for only a fraction of a second (about 10-6 seconds) before decaying (usually into an electron, and electron-antineutrino, and a muon neutrino). Discovery of the Muon Muons were discovered during the study of cosmic rays by Carl Anderson in 1936. They were discovered by studying how the particles in a cosmic ray bent within an electromagnetic field. Anderson noticed that some particles bent less sharply than electrons did, which meant they must have been heavier particles (and thus harder to deviate off of their original course by the same magnetic field strength). Most muons that exist in nature occur when pions (particles that are created in the collision of cosmic rays with particles in the atmosphere) decay. Pions decay into a muon and neutrinos.