The SINDRUM II experiment looks for the one-particle decay of this particle, and Louis Michel sometimes names the standard decay mode of this particle.  This particle was discovered by Street and Stevenson in a Wilson Cloud Chamber, and was at first conflated with the carrier of the residual strong force proposed by Yukawa.  The long lifetime of th
The SINDRUM II experiment looks for the one-particle decay of this particle, and Louis Michel sometimes names the standard decay mode of this particle.  This particle was discovered by Street and Stevenson in a Wilson Cloud Chamber, and was at first conflated with the carrier of the residual strong force proposed by Yukawa.  The long lifetime of this particle, two point two micro-seconds, is an important test of time dilation because this particle makes up most of the final decay product of cosmic rays that reach sea level.  The bound system of a positive form of this particle and an electron behaves like a hydrogen atom with one ninth the mass. For 10 points, name this lepton approximately two hundred times heavier than the electron.
The SINDRUM II experiment looks for the one-particle decay of this particle, and Louis Michel sometimes names the standard decay mode of this particle.  
Muon [accept Mu Meson from anyone who looks old enough to have been around when they still called it that]