This question is directed mostly at people who are expert in (beyond) standard model(s) of elementary particles, but input by other physicists or students is very much appreciated.

A friend asked me about a new discovery at CERN in March 2021 that I wasn't aware of it until now. Let me explain this discovery first. Quarks can decay into leptons and the standard model predicts that bottom (beauty) quarks would decay into muons at the same rate as they do into electrons. But, the experimental results of CERN reveal that the quarks appeared to decay into muon less often than they decayed into electrons (around 85 muon decays for every 100 electron decays). This evidence signals that some before unseen particle or a new force are involved in the decay process! As they claimed, this means the need for a better theory beyond the standard theory will become clearer.

If the experimental data are correct (according to the news, results are really strong since the uncertainty of the result is over three sigma, but not enough yet), what will be the properties of the new particle or (perhaps) the new force? This observation cannot be explained within the current state of physics?


I will turn my comment to an answer:

This is a CERN link discussing experimental tests of lepton universality . By itself this measurement is not sufficient since it is a 3.1 standard deviations. In particle physics only deviations over 5 are taken seriously as new discoveries. However there are more hints.

Lepton universality is the idea that all three types of charged lepton particles – electrons, muons and taus – interact in the same way with other particles. As a result, the different lepton types should be created equally often in particle transformations, or “decays”, once differences in their mass are accounted for. However, some measurements of particle decays made by the LHCb team and other groups over the past few years have indicated a possible difference in their behavior.

It is a hopeful violation of the Standard Model, to be used to get more data time. All higher energy experiments are efforts to find deviations from the SM, and get better theories but it is too early for conclusions.

Already there are theoretical papers attempting to fit the possible effect, for example . As far as I can understand they are not introducing a new force, the way GUTS model do, but they extend the group symmetries of the SM. So in their analysis there are no new forces, only new bosons due to the symmetry they propose to modify the standard model.

In this paper ,The role of the S3 GUT leptoquark in flavor universality and collider searches they attempt to use GUT theories to explain discrepancies, so no new to GUT forces are proposed.

There are new force particles expected in GUTs theories, generically noted as X (I suppose for "unknown") If a GUTS could fit the data (as the leptoquark claim above), it would imply that the particular GUTS model should be the real Standard, and after symmetry breaking, the present standard model with corrections appears. Then one should expect the X particle, after breaking, to exist with a large mass (similar to the Z and W existing after electroweak symmetry breaking) and should be searched for.

One has to wait for more data, and more theories :)

  • 1
    $\begingroup$ Thank you very much @annav (+1). LHCb collaboration in their paper emphasized that ""If [these results] confirmed by future measurements, this violation of lepton universality would imply physics beyond the Standard Model, such as a new fundamental interaction between quarks."" These really imply a new fundamental force? I'm interested in (supposing that the measurements are valid) what properties it may have and, e.g. besides the breaking of lepton universality, what would be the implications of the new fundamental interaction. I think that's an interesting question for many people. $\endgroup$
    – SG8
    Mar 29 at 6:29

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