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