Tau Decays Still Match Standard Model Expectations

While other experiments have shown what could be noise, or could be weak evidence of violations of lepton universality or lepton flavor violations, a new LHCb experiment paper finds no violations of lepton universality, no lepton flavor violations, no lepton number violations and no baryon number violations in tau lepton decays.

All of the tau lepton decays observed are in accord with the Standard Model expectation and the bounds on lepton or baryon number violations derived are very strict.  Tau leptons are also only about 1/3rd the mass of B mesons, so any lepton universality violation effect merely due to the high masses of the decaying particle should show up in tau lepton decays as well.

A study of pion decays released this past June likewise confirms lepton universality to high precision.

There has been weak evidence of lepton universality violations and lepton flavor non-conservation in B meson decays and Higgs boson decays, but those could just be statistical flukes or due to systemic error.  It is not easy to imagine why lepton universality might be violated with B meson decays, but not pion or tau lepton decays.