CERN's Large Hadron Collider
CERN's Large Hadron Collider

Subatomic particles have been discovered that seem to defy the Standard Model of particle physics. The team working at CERN’s Large Hadron Collider have discovered proof of leptons decaying at completely different rates, which could possibly point to some undiscovered forces.

Publishing their findings in the journal Physical Review Letters, the group from the University of Maryland had been searching for conditions and behaviors that don’t fit with the Standard Model. The model explains most known behaviors and interactions of fundamental subatomic particles, however it’s incomplete – for instance it doesn’t adequately explain gravity, dark matter and neutrino masses.

Researchers say the discovery of the non-conforming leptons might provide an enormous lead in the quest for non-standard phenomenon. The Standard Model concept of lepton universality assumes leptons are treated equally by fundamental forces.

The team looked at B meson decays including two kinds of leptons – the tau lepton and the muon, both of which are extremely 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. However the researchers discovered small but important variations in the predicted rates of decay.

This suggests there are undiscovered forces or particles interfering in the process. Study co-author Hassan Jawahery stated: “The Standard Model says the world interacts with all leptons in the same method. 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 have found evidence for non-standard physics.”

CERN’s Large Hadron Collider – Proton-proton collisions at the interaction point (far left) result in a shower of leptons and other charged particles. The yellow and green lines are computer-generated reconstructions of the particles’ trajectories through the layers of the LHCb detector.(CERN/LHCb Collaboration)

He said they’re now planning a range of different measurements in the hope of confirming their findings: “If this phenomenon is corroborated, we will have many years of work ahead. It could point theoretical physicists towards new ways to take a look at standard and non-standard physics.”

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 identical physical model: This replication provides an important independent check on the observations,” co-author Brian Hamilton mentioned. “The added weight of two experiments is the key here. This suggests that it isn’t just an instrumental effect–it’s pointing to real physics.”

Gregory Ciezarek, another co-author, added: “While these two results taken together are very promising, the observed phenomena will not be considered a true violation of the Standard Model with out further experiments to verify our observations.”

Jawahery stated that future work in this area will turn out to be ever more exciting, with specialists improving our understanding of how the universe evolved: “For example, we know that dark matter and dark energy exist, but we do not yet know what they’re or how to explain them. Our result could be a part of that puzzle. If we can demonstrate that there are missing particles and interactions beyond the Standard Model, it could help complete the picture.”


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