Abstract
Within the standard approach of effective field theory of weak interactions for varDelta B = 1 transitions, we look for possibly unexpected subtle New Physics effects, here dubbed “flavourful Easter eggs”. We perform a Bayesian global fit using the publicly available HEPfit package, taking into account state-of-the-art experimental information concerning these processes, including the suggestive measurements from LHCb of R_{K} and R_{K^{*}}, the latter available only very recently. We parametrise New Physics contributions to b rightarrow s transitions in terms of shifts of Wilson coefficients of the electromagnetic dipole and semileptonic operators, assuming CP-conserving effects, but allowing in general for violation of lepton flavour universality. We show how optimistic/conservative hadronic estimates can impact quantitatively the size of New Physics extracted from the fit. With a conservative approach to hadronic uncertainties we find nonzero New Physics contributions to Wilson coefficients at the level of sim 3sigma , depending on the model chosen. Furthermore, given the interplay between hadronic contributions and New Physics effects in the leptonic vector current, a scenario with nonstandard leptonic axial currents is comparable to the more widely advocated one with New Physics in the leptonic vector current.
Highlights
Easter eggs nowadays refer to inside jokes and/or secret messages usually hidden e.g. in computer gaming and hi-tech software
The tremendous progress of the experimental facilities has probed the flavour of the SM to an exquisite level of precision [2], along with the substantial effort on the part of the theoretical community to go well beyond leading order computations [3]. From this perspective of “precision tests”, radiative andleptonic ΔB = 1 processes, related at the partonic level to b → sγ, s transitions, occupy a special place in probing the SM and its possible extensions in terms of New Physics (NP) models [4,5]. These rare B meson decays belong to the class of flavour-changing neutral current (FCNC) processes, which are well known to be sensitive probes of Physics Beyond the Standard Model (BSM): – within the SM – the flavour structure of the theory allows FCNC to arise only at loop level, as a consequence of the GIM mechanism [6]
In this work, motivated by previous interesting findings concerning lepton flavour universality violation (LFUV) [69,70,71] and the measurement of RK and RK ∗, we focus on the contributions of NP appearing as shifts of the SM Wilson coefficients (WCs) related to the electromagnetic dipole and semileptonic operators with left-handed quark currents only
Summary
Easter eggs nowadays refer to inside jokes and/or secret messages usually hidden e.g. in computer gaming and hi-tech software. The tremendous progress of the experimental facilities has probed the flavour of the SM to an exquisite level of precision [2], along with the substantial effort on the part of the theoretical community to go well beyond leading order computations [3] From this perspective of “precision tests”, radiative and (semi)leptonic ΔB = 1 processes, related at the partonic level to b → sγ , s transitions, occupy a special place in probing the SM and its possible extensions in terms of New Physics (NP) models [4,5].
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