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CERN experiments put Standard Model to stringent test

Posted July 22, 2013

New results to be presented at the EPS-HEP conference in Stockholm, Sweden, this afternoon have put the Standard Model of particle physics to one of its most stringent tests to date. The CMS and LHCb experiments at CERN’s1 Large Hadron Collider will present measurements of one of the rarest measureable processes in physics: the decay of a Bs (pronounced B-sub-s) particle into two muons.

The new measurements show that only a handful of Bs particles per billion decay into pairs of muons. Because the process is so rare, it is an extremely sensitive probe for new physics beyond the Standard Model2. Any divergence from the Standard Model prediction would be a clear sign of something new.

Both experiments will present results to a very high level of statistical significance (over 4 sigma for each experiment). These results are in good agreement with the Standard Model.

“This is a great result for LHCb,” says the collaboration’s spokesperson Pierluigi Campana. “It’s precisely for measurements like this that LHCb was built. This result shows that we’re really putting the Standard Model to the most stringent test yet at LHC energies, and so far it’s coming through with flying colours.”

The Standard Model has been pieced together over a period of over 40 years. It is a remarkably successful theory that accurately predicts the behaviour of the fundamental particles, and has been put to the test experimentally with great precision. But the Standard Model is not the end of the story: it does not account for gravity, for example, and it does not describe the so-called dark universe. Only around 5% of our universe consists of the kind of visible matter described by the Standard Model. The rest is made up of dark matter and energy, whose presence is deduced from the influence they have on the ordinary, visible matter.

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