New Physics in $${\varvec{b \rightarrow s \ell ^+ \ell ^-}}$$ confronts new data on lepton universality

Abstract

In light of the very recent updates on the R K and R K * measurements from the LHCb and Belle collaborations, we systematically explore here imprints of New Physics in b → s + − transitions using the language of effective field theories. We focus on effects that violate Lepton Flavour Universality both in the Weak Effective Theory and in the Standard Model Effective Field Theory. In the Weak Effective Theory we find a preference for scenarios with the simultaneous presence of two operators, a left-handed quark current with vector muon coupling and a right-handed quark current with axial muon coupling, irrespective of the treatment of hadronic uncertainties. In the Standard Model Effective Field Theory we select different scenarios according to the treatment of hadronic effects: while an aggressive estimate of hadronic uncertainties points to the simultaneous presence of two operators, one with left-handed quark and muon couplings and one with left-handed quark and right-handed muon couplings, a more conservative treatment of hadronic matrix elements leaves room for a broader set of scenarios, including the one involving only the purely left-handed operator with muon coupling.

Implications for new physics in $$b\rightarrow s \mu \mu $$ transitions after recent measurements by Belle and LHCb

“…For the scans with 1 or 2 independent Wilson coefficients, our results are in good agreement with those reported in Refs. [25][26][27][28][29]. In general, we observe slightly lower bestfit point values of the coefficient C µ 9 .…”

“…In concomitance with our work, Refs. [25][26][27][28][29] have recently appeared, most of which analyze the effect of incorporating the new LHCb and Belle data in a frequentist con-text. The part of our analysis based on the chi-squared distribution agrees with those studies, but we repeat that we focus in this article on the computation of the multi-dimensional Bayesian posterior pdf, and on the use of Bayes factors to discriminate among models.…”

∆Ms theory precision confronts flavour anomalies

“…On the other hand, the recent update of R K at Moriond 2019 [42] favours a non-zero RH quark current contribution, as widely discussed in the literature since then (see e.g. [54][55][56][57][58][59][60]). There is however a problem with this solution, which is that in our Z model, at the leading order in the NP contribution, the behaviour can be written as has shrunk by only a small amount, and so our benchmark point is only marginally more favoured.…”

“…Intriguingly, one obtains a very good description of the b → s data by allowing new physics only in a single combination of Wilson coefficients (for recent fits see e.g. [54][55][56][57][58][59][60]). The best-fit scenario δC µ 9 = −δC µ 10 ≈ −0.53 ± 0.08 of [54] corresponds to an effective operator with left-handed (LH) quark and muon currents and we consider its interplay with ∆M s in Section 3.4.…”

Explaining b→sℓ+ℓ− data by sneutrinos in the R -parity violating MSSM

“…Finally, LHCb has also observed a 3.3σ deficit in the B 0 s → ϕμ þ μ − decay [20,21]. Motivated by these deviations and using the other available data on such rare b → sl þ l − transitions, many global analyses have been carried out [19,[22][23][24][25][26][27][28], finding that a negative shift in a single Wilson coefficient of local operator like O μμ 9 ¼ ðsγ α P L bÞðμγ α μÞ or O μμ LL ¼ ðsγ α P L bÞðμγ α P L μÞ leads to a consistent description of the data, with the corresponding best-fit point can improve the fit to the data by more than 5σ compared to the SM. Furthermore, the operator O μμ LL performs better than O μμ 9 , mainly because there is now ∼2σ tension in the branching fraction of B s → μ þ μ − [22,[29][30][31][32][33][34], which is not affected by O μμ 9 .…”