The Standard Model has some gaps and is unable to explain phenomena like dark matter or gravitational interaction between particles. Some physicists are seeking what they call "New Physics", something more fundamental, but there has been no direct proof of its existence, only indirect observation of dark matter, as deduced, among other things, from the movement of the galaxies.

A team of physicists from the Universitat Autònoma de Barcelona and the French CNRS have predicted deviations in the probability of one of the B meson decays that have been detected experimentally in the LHC accelerator at CERN. Confirmation of these results would be the first direct evidence of the existence of the 'New Physics', they say.  At CERN there are four experiments, four large detectors (ATLAS, CMS, LHCb, and Alice) that record collisions between particles so that scientists can study their behavior. The LHCb detector is designed to study the behavior of quarks and what are known as rare decays, which are very infrequent. 

New Physics implies the existence of deviations in the probability of a very specific decay of the B meson, they say, and detecting these small deviations through an experiment would be the first direct proof of the existence of New Physics.

At the EPS 2013 international conference on particle physics in July, scientists at the LHCb detector, one of the large experiments being conducted by the CERN's LHC accelerator, presented the results of the experimental measurements of the B meson decay. The measurements showed deviations with respect to the predictions of the Standard Model that were previously calculated by UAB and CNRS researchers. They say they have proved that all these deviations show a coherent pattern and that has allowed them to identify their origin from a unique source.

The results of their analysis point to a deviation from the Standard Model prediction of 4.5 sigmas. If confirmed, this is a significant event. 

Joaquim Matias (left) and Javier Virto at the Universitat Autònoma de Barcelona (UAB). Credit: UAB

“We must be prudent, because more studies and more experimental measurements will be needed for confirmation," says Joaquim Matias, "but if they are confirmed this is the first direct proof of New Physics, a more general theory than the current Standard Model. If the Higgs completed the Standard Model puzzle, these findings could be the first piece in an even bigger puzzle."

The researchers claim that one of the New Physics models that could explain these results would be the one that postulates the existence of a new particle named Zprima, "but there could be lots of compatible models," points out Matias.

Scientists at the other main LHC experiment, the CMS detector, also want to take these measurements and they have invited Matias to explain the theoretical details in a seminar to see it the results can be corroborated. At the same time, LHCb is also adding new data to improve the statistics and confirm the measurements next March.

Beyond the Standard Model

For years, particle physicists have known that the Standard Model lacks a candidate for dark matter. In addition, critics note other problems, such as the so-called fundamental problem of hierarchies or the matter-antimatter asymmetry of the universe.

Two of the central goals of the Large Hadron Collider (LHC) at CERN are finding the Higgs boson and finding what is called New Physics, a more fundamental and general theory than that of the Standard Model in which the latter would be just one particular case. Just a year ago, the Higgs boson was discovered, but the particle seems to fit perfectly into the Standard Model and currently gives us no clues regarding New Physics.

Results presented in the EPS 2013 conference

On July 19th July at EPS 2013, Matias presented the theoretical predictions of his research team on one of these decays: that of a B meson, formed by a b quark and a d antiquark, into a pair of muons and a particle called K*. The UAB and CNRS researchers calculated and predicted how this decay should work and how it should change in different New Physics scenarios.

Shortly afterwards, an experimental physicist from the LHCb detector, Nicola Serra, presented the first completed experimental results of that decay. Surprisingly, the experimental measurements were consistent with the deviations predicted by Matias and his collaborators. For the first time, deviations of this type were consistent with theoretical predictions based on the presence of contributions that transcends the Standard Model. 

Also participating in the study were Javier Virto, from the UAB's Department of Physics, and Sebastien Descotes-Genon from the University of Paris-Sud 11.