CERN is hard at work testing the very limit of our particle physics theory, the Standard Model, and new data analyses indicate that we are very close to seeing what lies beyond. This week, there was an announcement that the LHCb collaboration saw an anomaly in B0 meson decays.
Mesons are particles made of two quarks (unlike protons that are made of three, for example). The B0 is made of a down quark and an antibottom quark. It decays by turning into another meson, a kaon, and another pair of particles (either electrons or muons).
Muons are just heavy version of the electrons, same everything but 200 times more massive. This is what the Standard Model tells us. Electrons and muons share “lepton universality”, which means we should be able to predict how often we see B mesons turn into muons. The Standard Model gives a well-defined value. But surprisingly, this is not seen in the experiment. The mesons turns into muons less often.
This is a tantalizing hint to physics beyond the Standard Model. But it is important to remember that it is just a hint. The discrepancy has been witnessed at the level of 2.2 and 2.5 sigmas. That’s between a 98.6 and 99.4 percentage that the anomaly is not a fluke. That might seem like good odds, but they are not good enough for scientific standards.
Just last year, a mysterious “bump” in the data appeared to have better odds than these discrepancies and it turned out to be nothing. The spotlight is now on the LHCb experiment to strengthen these results. B0 mesons have long been thought to be a great testing ground for new physics and it might soon deliver on that notion.
The Standard Model has brought forward incredible discoveries predicting the existence of particles, like the Higgs Boson, before we had the technology to go look for them. However, it does have limitations, as it doesn’t include gravity for example.
1