LHC finds subatomic particles that may defy the Standard Model

Scientists conducting experiments at the CERN Large Hadron Collider (LHC) have found new evidence of subatomic particles treated in strange ways not predicted by the Standard Model of particle physics, a potentially significant find in the search for non-standard phenomena.

The research team, whose findings will appear in the September 4 edition of the Physical Review Letters, looked at data collected by the LHCb detector during the first run of the particle collider back in 2011 and 2012. They analyzed B meson decays, which are processes that produce lighter particles including two types of leptons: the tau lepton and the muon.

Unlike electrons, which are stable leptons, tau leptons and muons are highly unstable and decay in less than a second, the study authors explained. A Standard Model concept known as “lepton universality” assumes that leptons are treated equally by all fundamental forces, meaning that the tau lepton and the muon should decay at the same rate, once corrected for differences in mass.

However, the team discovered a slight but noticeable difference in the predicted rates of decay, which suggests that there could be some yet-undiscovered particle or force that is interfering in this process. The new discovery appears to directly violate the rules of the Standard Model.

Findings, if corroborated, may be evidence of non-standard physics

“The Standard Model says the world interacts with all leptons in the same way,” co-author and University of Maryland professor Hassan Jawahery explained. “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,” Jawahery said, adding that if their findings are corroborated, “we will have decades of work ahead.” The findings potentially may help physicists uncover “new ways to look at standard and non-standard physics.”

The results of this new experiment join a similar lepton decay finding previously detected at the BaBar experiment at the Stanford Linear Accelerator Center, which suggested a similar deviation from Standard Model predictions, the study authors said. Both experiments involved the decay of B mesons, but they differed in the types of collisions driving their findings, they added.

“The experiments were done in totally different environments, but they reflect the same physical model. This replication provides an important independent check on the observations,” explained study co-author Brian Hamilton of UMD. “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.”

“While these two results taken together are very promising, the observed phenomena won’t be considered a true violation of the Standard Model without further experiments to verify our observations,” added co-author Gregory Ciezarek, a physicist at the Dutch National Institute for Subatomic Physics (NIKHEF).

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Image credit: EurekAlert/CERN/LHCb Collaboration