In their namesake “puzzle,” these particles have a higher-than-expected detection rate (-5[1])in the LHC Forward experiment. The Higgs boson was discovered by both the ATLAS collaboration and the Compact Solenoid detector named for these (10[1])particles. An inconsistency in the Standard Model is the 3.5-standard-deviation discrepancy between this particle’s measured and predicted g-factor. (10[1])By increasing the reduced mass of hydrogen, these particles are hypothesized to catalyze a type of cold fusion. The Rossi–Hall experiment (-5[1])showed time dilation (10[1])by observing discrepancies in the 2.2-microsecond decay time of these particles after they were produced in the atmosphere by cosmic rays. For 10 points, (-5[1])name this (-5[1])unstable lepton with a mass between that of the tauon and electron. ■END■ (10[3]0[2])