Understanding the B→K*μ⁺μ^- anomaly

We present a global analysis of the B→K*(→Kπ) μ+μ- decay using the recent LHCb measurements of the primary observables P1,2 and P4,5,6,8′. Some of them exhibit large deviations with respect to the Standard Model (SM) predictions. We explain the observed pattern of deviations through a large new physics contribution to the Wilson coefficient of the semileptonic operator O9. This contribution has an opposite sign to the SM one, i.e., reduces the size of this coefficient significantly. A good description of data is achieved by allowing for new physics contributions to the Wilson coefficients C7 and C9 only. We find a 4.5σ deviation with respect to the SM prediction, combining the large-recoil B→K*(→Kπ) μ+μ- observables with other radiative processes. Once low-recoil observables are included the significance gets reduced to 3.9σ. We have tested different sources of systematics, none of them modifying our conclusions significantly. Finally, we propose additional ways of measuring the primary observables through new foldings. © 2013 American Physical Society.