New physics in b →se+e- ?

Abstract

At present, the measurements of some observables in B→K∗μ+μ- and Bs0→φμ+μ- decays, and of RK(∗)≡B(B→K(∗)μ+μ-)/B(B→K(∗)e+e-), are in disagreement with the predictions of the standard model. While most of these discrepancies can be removed with the addition of new physics (NP) in b→sμ+μ-, a difference of 1.7σ still remains in the measurement of RK∗ at small values of q2, the dilepton invariant mass squared. In the context of a global fit, this is not a problem. However, it does raise the question: if the true value of RK∗low is near its measured value, what is required to explain it? In this paper, we show that, if one includes NP in b→se+e-, one can generate values for RK∗low that are within ∼1σ of its measured value. Using a model-independent, effective-field-theory approach, we construct many different possible NP scenarios. We also examine specific models containing leptoquarks or a Z′ gauge boson. Here, additional constraints from lepton-flavor-violating observables, Bs0-Bs0 mixing, and neutrino trident production must be taken into account, but we still find a number of viable NP scenarios. For the various scenarios, we examine the predictions for RK(∗) in other q2 bins, as well as for the observable Q5≡P5′μμ-P5′ee.