A once-promising hint of new physics from the Large Hadron Collider (LHC), the world’s largest particle accelerator, has faded, crushing one of physicists’ best hopes for a major discovery.
The apparent anomaly is an unexpected difference between the behavior of electrons and that of their more massive cousins, muons, when they arise from the decay of certain particles.
But new results from the LHCb experiment at CERN, the European particle physics laboratory near Geneva, Switzerland, show that electrons and muons are produced at the same rate.
“My first impression was that the analysis was more reliable than before,” says Florencia Canelli, an experimental particle physicist at the University of Zurich in Switzerland and a senior member of another LHC experiment. It reveals how some surprising subtleties come together to produce apparent anomalies, she said.
LHCb physicist Renato Quagliani of the Swiss Federal Institute of Technology in Lausanne reported the results on December 20 at a CERN workshop that attracted more than 700 online viewers. The LHCb collaboration also published two preprints on the arXiv repository.
unbalanced attenuation
Small differences in muon and electron production were first reported at the LHCb in 2014.When protons collide to produce Second Mesons, these decay quickly. The most common modes of decay produce another kind of meson, called a meson, plus pairs of particles and their antiparticles—an electron and a positron, or a meson and an antimeson. The Standard Model predicts that these two types of pairs should occur with roughly equal frequency, but the LHCb data suggest that electron-positron pairs occur more frequently.
Particle physics experiments often yield early results that deviate slightly from the Standard Model, but as the experiment collects more data, it turns out to be just a statistical fluke. But this time it didn’t happen. On the contrary, over time, Second– The meson anomaly appears to have become more pronounced, reaching a confidence level known as 3 sigma – although it still falls short of the level of significance commonly used to declare a discovery, ie 5 sigma.some related measurements Second Mesons also revealed deviations from theoretical predictions based on the Standard Model of particle physics.
Results reported this week include more data than previous LHCb measurements Second– Meson decay, and a more thorough study of possible confounding factors. LHCb spokesman Chris Parkes, a physicist at the University of Manchester in the United Kingdom, said the stark discrepancy in earlier measurements involving muons was partly due to misidentifying some other particles as electrons. Although LHC experiments are good at capturing muons, they are harder to detect electrons.
retarget search
The results are likely to disappoint many theorists who spend their time trying to come up with models that could explain the anomaly. “I’m sure people would expect us to find a hole in the standard model,” Parks said, but in the end, “you can do the best analysis you can with the data you have, and then you’ll see what nature gives you.” ,He said. “That’s really how science works.”
Gino Isidori, a theoretical physicist at the University of Zurich who attended the CERN talk, said that while the latest result had been rumored for months, its confirmation was surprising because of the associated anomalies A coherent picture seems to be forming.This could indicate the presence of previously unseen elementary particles influencing decay Second meson. Isidori praises the LHCb collaboration for being “honest” in acknowledging that its previous analysis was flawed, but he regrets that it took so long for the collaboration to discover the problem.
However, some other exceptions, including some documented in SecondMeson decays that don’t involve mesons could still be real, Isidori added. “Not all is lost.”
Marcella Bona, an experimental physicist at Queen Mary University of London who is part of another LHC experiment, agrees. “It looks like theorists are already thinking about how to comfort themselves and refocus.”
The remaining promising hints of new physics include a discovered measurement The mass of a particle is called W Bosons are bigger than expected, announced in April. But a separate anomaly, also involving muons, might disappear. The muon’s magnetic moment appears to be stronger than the Standard Model predicts, but The latest theoretical calculations show that it is not, after all. Instead, the discrepancy likely stems from a miscalculation of standard model forecasts.
This article is reproduced with permission, has been reprinted first published December 20, 2022.
