In their namesake “puzzle,” these particles have a higher-than-expected detection rate in the (-5[1])LHC Forward experiment. The Higgs boson was discovered by both the ATLAS collaboration and the Compact (10[1])Solenoid detector named for these particles. An inconsistency in the Standard Model is the 3.5-standard-deviation discrepancy between this particle’s measured and predicted (10[1]-5[1])g-factor. By increasing the reduced mass of hydrogen, these particles are hypothesized to catalyze a type of cold fusion. The Rossi–Hall experiment showed time dilation by observing discrepancies in the 2.2-microsecond (-5[1])decay time of these particles after they were produced in the atmosphere by cosmic rays. For 10 points, name this unstable lepton with a mass between that of the tauon and electron. (10[1])■END■ (10[1]0[1])