A signal from the Large Hadron Collider (LHC) could challenge the standard model of particle physics for how matter and forces interact.
The LHCb experiment at CERN, Europe's particle-physics lab near Geneva, has uncovered an unexpected difference in the rate at which short-lived particles called B mesons undergo certain decays into muons and taus (heavier cousins of the electron). The standard model says that once the particles' mass differences are taken into account, the decays should occur at exactly the same rate.
The deviation is small, and the chance that it is a statistical fluctuation in random noise is too high to claim a discovery (the significance is 2.1 sigma, but physicists' threshold for a discovery is 5 sigma). However, the results are intriguing because they match previous measurements made by two other experiments elsewhere.
Phys. Rev. Lett. (in the press) http://journals.aps.org/prl/accepted/8e07cYdfSd71f65779771c1232551e3be1270df73