Implications for new physics in brightarrow s mu mu transitions after recent measurements by Belle and LHCb

Kamila Kowalska,Enrico Maria Sessolo,Dinesh Kumar

doi:10.1140/epjc/s10052-019-7330-2

Kamila Kowalska, Enrico Maria Sessolo + Show 1 more

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https://doi.org/10.1140/epjc/s10052-019-7330-2

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Abstract

We present a Bayesian analysis of the implications for new physics in semileptonic brightarrow s transitions after including new measurements of R_K at LHCb and new determinations of R_{K^*} and R_{K^{*+}} at Belle. We perform global fits with 1, 2, 4, and 8 input Wilson coefficients, plus one CKM nuisance parameter to take into account uncertainties that are not factorizable. We infer the 68% and 95.4% credibility regions of the marginalized posterior probability density for all scenarios and perform comparisons of models in pairs by calculating the Bayes factor given a common data set. We then proceed to analyzing a few well-known BSM models that can provide a high energy framework for the EFT analysis. These include the exchange of a heavy Z^{'} boson in models with heavy vector-like fermions and a scalar field, and a model with scalar leptoquarks. We provide predictions for the BSM couplings and expected mass values.

Highlights

The LHCb Collaboration has recently presented a new measurement of the observable RK, the ratio of the branching fraction of B-meson decay into a kaon and muons, over the decay to a kaon and electrons, from the combined analyses of the Run 1 and partially of Run 2 data set [1], which readsRK = 0.846+−00..006504−+00..001146. (1)This new measurement of RK is compatible with the Standard Model (SM) prediction at 2.5 σ significance
Parameter New Physics (NP) scenario the 2-parameter model in in has become The reason favored over can be inferred, again, from Eqs. (10)–(11): since RK and RK ∗ are expected to be equal in the C9μ, C1μ0 model and instead the new measurement of RK shows a slight shift towards the SM value, this scenario receives a penalty with respect to the previous determination
In this paper we have presented a global Bayesian analysis of the NP effects on effective operators of semileptonic b → s transitions after the very recent updated measurement of RK at LHCb and new results for the observable RK ∗ in B0-meson decays, as well as the first measurement of its counterpart RK ∗+ in B+ decays at Belle

Summary

Introduction

The LHCb Collaboration has recently presented a new measurement of the observable RK , the ratio of the branching fraction of B-meson decay into a kaon and muons, over the decay to a kaon and electrons, from the combined analyses of the Run 1 and partially of Run 2 data set [1], which reads. The update of the LHCb results had been long awaited, as Run 1 determinations of RK and RK ∗ [3,4] both featured a 2–3 σ deficit with respect to the SM They were part of a broader set of anomalous measurements in rare semileptonic B decays obtained at the LHC and Belle [5,6,7,8,9,10], which involved b → s transitions and muons in the final state, and which in global statistical analyses [11,12,13,14,15,16,17,18,19,20,21,22] had been shown to favor strongly the presence of a few NP operators over the SM.

Fit methodology

Effective field theory analysis

Discussion of results

Heavy Z

Leptoquarks

Summary and conclusions