Tread Carefully Around the Hype: Leptons Behaving Badly at the LHC

Subatomic particles have been found that appear to defy the Standard Model of particle physics. The team working at Cern's Large Hadron Collider have found evidence of leptons decaying at different rates, which could possibly point to some undiscovered forces.

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.

This suggests there are undiscovered forces or particles interfering in the process. Study co-author Hassan Jawahery said: "The Standard Model says the world interacts with all leptons in the same way. There is a democracy there. But there is no guarantee that this will hold true if we discover new particles or new forces. Lepton universality is truly enshrined in the Standard Model. If this universality is broken, we can say that we've found evidence for non-standard physics."

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Check your instruments.  Last tim something like this happened, it turned out to be dirty fiber optics.