New physics in $b\to s$ transitions after LHC run 1

TL;DR

This paper analyzes rare $b o s$ decay data, finds tensions with the Standard Model, and explores potential new physics explanations, emphasizing lepton flavour universality violations and proposing future tests.

Contribution

It provides a comprehensive global fit of $b o s$ decay data, assesses theoretical uncertainties, and discusses implications for new physics models including supersymmetry and $Z'$ bosons.

Findings

Significant tensions between data and Standard Model predictions.

Lepton flavour universality violation hints in current measurements.

Predictions for future observables to distinguish new physics scenarios.

Abstract

We present results of global fits of all relevant experimental data on rare $b \to s$ decays. We observe significant tensions between the Standard Model predictions and the data. After critically reviewing the possible sources of theoretical uncertainties, we find that within the Standard Model, the tensions could be explained if there are unaccounted hadronic effects much larger than our estimates. Assuming hadronic uncertainties are estimated in a sufficiently conservative way, we discuss the implications of the experimental results on new physics, both model independently as well as in the context of the minimal supersymmetric standard model and models with flavour-changing $Z'$ bosons. We discuss in detail the violation of lepton flavour universality as hinted by the current data and make predictions for additional lepton flavour universality tests that can be performed in the future. We find that the ratio of the forward-backward asymmetries in $B \to K^* \mu^+\mu^-$ and $B \to K^* e^+e^-$ at low dilepton invariant mass is a particularly sensitive probe of lepton flavour universality and allows to distinguish between different new physics scenarios that give the best description of the current data.