Unexplained results captivate physicists with the world’s largest particle collider

Editor’s Note (10/19/21): On October 19, 2021, LHCb physicists revealed two minor anomalies that continued the strange pattern of “lost” muons. This is the expected rate for these exotic subatomic particles. With further verification, these results could be the most promising paths to new physics beyond the Standard Model.

If beauty is in the eyes of the beholder, consider the fascinating new results that mislead the world’s particle physicists. Specifically, scientists are interested in fresh data from the LHCb (Large Hadron Colliderbeauty) detector. NS-Mesons-Particles containing beauty quarks. Nearly 1,000 physicists monitored the LHCb collaboration during a virtual session of the annual Rencontres de Moriond conference on Tuesday. Published evidence Due to unexplained contradictions in the behavior of electrons and their heavier cousins, muons.

Under the Standard Model (the theory that describes elementary particles and the forces they follow minus gravity), leptons such as electrons and muons Same except for their mass. Therefore, the B meson should decay into the kaon and the two muons at the same rate as it decays into the kaon and the two electrons. However, LHCb makes a difference in this rare beauty collapse. B mesons appear to decay into muons 15% less frequently than electrons.

“This new measurement is certainly interesting,” says Monica Blanke, a theoretical physicist at the Karlsruhe Institute of Technology in Germany, who was not involved in the new study. “When finally confirmed experimentally, there is actually something beyond the Standard Model that treats lepton flavors differently.”

Physicists have long wondered if muons, electrons, and other leptons make a difference other than mass. The latest LHCb results suggest that the answer may be “yes”. This finding has a statistical significance of 3.1 sigma and meets the standard baseline of evidence in particle physics. To be precise, 3.1 sigma means that statistical variability allows researchers to see inconsistencies between electrons and muons, even in the absence of new physics. 15% or more The experiment was conducted once every 740 times. This seems to suggest that the observed muon-electron discrepancy is almost certainly more than a sigma, but in reality, the 3-sigma effect is the gold standard of discovery in particle physics. It is well below 5 sigma. After 3.4 million experiments, such a large statistical fluke was seen. (These numbers are subtle but important Different from 1/740 or 1 / 3.4 million chances It’s wrong. )

Why do you make a fuss about statistics? In LHCb and other experiments, two-sigma and three-sigma discrepancies between electrons and muons have appeared over the years. But so far, none of these results have been maintained. When the data was collected again, the differences between the leptons diminished and the Standard Model won.

“I wasn’t too excited if there was only one. I’ve seen the other anomalies go away,” said Gino Ishidori, a theoretical physicist at the University of Zurich who wasn’t involved in the study. Says. But he is encouraged by the latest LHCb results. Because it follows other measurement patterns that suggest the difference between electrons and muons.That’s a good reason for Ishidori and other particle physicists. Careful excitement..

Beauty thing

Located on the French-Swiss border, the LHCb is one of many detectors along the 17-mile loop of the Large Hadron Collider (LHC). LHCb also examines the results of proton-proton collisions, but its focus is on very rare decays such as B mesons.

“Rare decay is another way to try to find heavy particles,” says Patrick Koppenburg, a particle physicist at LHCb. Instead of crushing protons and looking for signs of new particles in detritus, as when the LHC successfully brute-forced the Higgs boson, the LHCb looks for subtle fluctuations in one-millionth of the event. That is, the rare decay of B mesons does not directly produce new particles. Muons and kaons are old hats, but the rate at which collapse occurs can depend on heavy particles that are not yet visible, affecting behind-the-scenes results. For example, in the 1960s, a rare decay of kaons suggested the existence of a charm quark before it was discovered directly. LHCb is designed to pull these needles out of a pile of hay. However, it is still difficult to work with and full of experimental uncertainty.

Second, there are theoretical uncertainties to consider. A prediction of the Standard Model where researchers compare results. Part of the excitement surrounding the latest LHCb results is that the breakdown of certain B mesons is “clean”. The theoretical uncertainty is very small. By eliminating one source of error, you can easily see if the difference between an electron and a muon is real.

Since the beginning of the Standard Model in the 1970s, theoretical physicists have proposed models that explain this difference in the form of new particles. The two top candidates are Z'(pronounced “G-Prime”), a variation of the existing Z boson, and leptoquark, a particle that connects leptons and quarks. In the coming days and weeks, theorists will update their models with the latest results.In fact, three Preprint paper It was Already released Within 24 hours after the LHCb results were announced.

However, the physics of this rare decay has not yet been resolved, and much more data is needed before claiming that the new particles are the cause. The best option for confirmation is the Japanese experiment Bell II. Mikihiko Nakao, a researcher involved in Bell II, predicts that it will take about five years to catch up with the sensitivity of LHCb.

Currently, LHCb is shut down for maintenance. But resuming with an upgraded detector next year could double all the data retrieved in the last decade, according to Koppe-Berg, in just one year. In April, future results of the Muon g-2 experiment at the Fermi National Accelerator Laboratory in Batavia, Illinois may also shed light on the differences between leptons.

Physicists are aware that this latest result (data uplift) may only be a statistical variation. Disappointed several times before, they are careful to hedge their bets so as not to convey certainty or excessive hype.

But if it’s real, well, it would be beautiful. Unexplained results captivate physicists with the world’s largest particle collider

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