Publishing their findings in the journal Physical Review Letters, the team from the University of Maryland had been searching for conditions and behaviours that do not fit with the Standard Model. The model explains most known behaviours and interactions of fundamental subatomic particles, but it is incomplete – for example it does not adequately explain gravity, dark matter and neutrino masses.
Researchers say the discovery of the non-conforming leptons could provide a big lead in the search for non-standard phenomenon. The Standard Model concept of lepton universality assumes leptons are treated equally by fundamental forces.
They looked at B meson decays including two types of leptons – the tau lepton and the muon, both of which are highly unstable and decay within just a fraction of a second. The tau lepton and muon should decay at the same rate after mass differences are corrected. But the researchers found small but important differences in the predicted rates of decay.
Researchers also noted their research add to previous findings about lepton decay – BaBar experiment - with both experiments (carried out in very different environments) showing the same physical model: This replication provides an important independent check on the observations," co-author Brian Hamilton said. "The added weight of two experiments is the key here. This suggests that it's not just an instrumental effect--it's pointing to real physics."