Researchers at three experimental facilities in Japan, the US, and Europe have discovered anomalies in the decay of a rare particle called a B meson that suggests that physics doesn’t appear to work the way we expected it to.
The anomalous decay violates the principle of lepton universality. This is where electrons and their two massive cousins, the muons and tau particles, behave in the same way. The only difference is their masses and lifetimes. According to a study reported in Nature, however, there’s something else going on. The rates for some decays of the heavy lepton tau, relative to the light leptons, were higher than predictions.
Particle physics is described by one of the greatest theories ever produced, called the Standard Model. While so far it has been successful in explaining and predicting phenomena and particles (like the Higgs boson), it is still limited. For example, it doesn’t include gravity. Particle physicists, therefore, have been looking for violations of the Standard Model in the hopes of finding new physics.
“We saw the first significant observation of something beyond the Standard Model at the BaBaR experiment conducted at the SLAC National Accelerator Laboratory,” co-author Manuel Franco Sevilla said in a statement.
The BaBaR results are in agreement with findings from the Belle experiment in Japan and recent results from CERN. When the data from the three experiments are considered together, they bring a violation of the lepton universality to a 99.95 percent certainty. This is pretty good, but not enough to qualify as a discovery.
A discovery needs to reach a level of certainty of 99.9999 percent to pass the stringent (but justified) scientific standards. That's with good reason as there have been examples of false positives, like the infamous CERN bump a few years ago. So while the results are promising, it’s important not to count our chickens before they hatch.
More investigations of the B meson decays will be conducted to either confirm or disprove what has been seen so far. If they are confirmed, this would mean new, unexpected physics is out there. Future experiments will look explore why the lepton universality doesn’t work as we expected.
"We're not sure what confirmation of these results will mean in the long term," Franco Sevilla added. "First, we need to make sure that they're true and then we'll need ancillary experiments to determine the meaning."
We will have to wait and see, but the Standard Model might still have some tricks up its sleeves.