Past exam of the particle and nuclear physics course of the University of Cambridge / 2015 / Paper 1 / 3 / c / Solution

The entrance Yukawa coupling is proportional to the incident lepton mass, so the partial Higgs width into that lepton pair is proportional to its mass squared. With the question's masses,The same factor enhances direct s-channel Higgs boson formation when all other factors are held fixed. The much larger muon Yukawa coupling motivates a muon-collider Higgs resonance. Heavier muons also radiate less strongly in a curved orbit, but their decay lifetime makes a collider technically demanding. The resonance remains narrow, so a sufficiently small beam-energy spread is essential to retain a large fraction of the ideal peak.