31.05.2021Updated measurement of Bs decay confirms discrepancy with Standard Model

The decay B_s-->phimumu is rare b->sll transition, which is suppressed in the Standard Model and therefore highly sensitive to new physics. An updated measurement of the branching fraction (decay probability) has been recently been made public in a recent paper with Ambizone fellow Eluned Smith having a leading role in the measurement. The results point towards a 3.6 sigma deviation from SM predictions, where the branching fraction is smaller than predicted by theory. While dependent on theoretical uncertainties from QCD, the result is coherent with other rare b->sll decays anomalies that recently caused excitement due to possible violations of lepton universality (see here for more details).  

Patrick Owen