A challenge to lepton universality in B-meson decays

One of the key assumptions of the standard model of particle physics is that the interactions of the charged leptons, namely electrons, muons and taus, differ only because of their different masses. Whereas precision tests comparing processes involving electrons and muons have not revealed any definite violation of this assumption, recent studies of B-meson decays involving the higher-mass tau lepton have resulted in observations that challenge lepton universality at the level of four standard deviations. A confirmation of these results would point to new particles or interactions, and could have profound implications for our understanding of particle physics. Recent measurements of B-meson decays in which tau leptons are produced might challenge the standard model assumption that interactions of leptons differ only because of their different masses. The standard model of particle physics is incomplete because it cannot explain phenomena such as dark matter. At particle colliders like the Large Hadron Collider (LHC) at CERN, physicists are looking for clues to how the standard model could be amended. But so far the LHC has produced only a few results that represent good leads. One type of experiment that has revealed cracks in the standard model involves high-precision measurements of flavor-changing neutral currents involving beauty quarks. Focusing on the on-going efforts at the LHC, the authors review recent such measurements and discuss whether the discrepancies found hint at new particles that have yet to be discovered.