Explaining the $$R_K$$ R K and $$R_{K^*}$$ R K ∗

Abstract

Recent LHCb results on R K * , the ratio of the branching fractions of B → K * μ + μ − to that of B → K * e + e − , for the dilepton invariant mass bins q 2 ≡ m 2 = [0.045-1.1] GeV 2 and [1.1-6] GeV 2 show approximately 2.5σ deviations from the corresponding Standard Model prediction in each of the bins. This, when combined with the measurement of R K (q 2 = [1 − 6] GeV 2 ), a similar ratio for the decay to a pseudo-scalar meson, highly suggests lepton non-universal new physics in semi-leptonic B meson decays. In this work, we perform a model independent analysis of these potential new physics signals and identify the operators that do the best job in satisfying all these measurements. We show that heavy new physics, giving rise to q 2 independent local 4-Fermi operators of scalar, pseudo-scalar, vector or axial-vector type, is unable to explain all the three measurements simultaneously, in particular R K * in the bin [0.045-1.1], within their experimental 1σ regions. We point out the possibility to explain R K * in the low bin by an additional light ( 20 MeV) vector boson with appropriate coupling strengths to (b s) and (ē e).

Light resonances and the low-q2 bin of $$ {R}_{K^{*}} $$

“…[11][12][13][14][15][16][17][18]. In this work, we point out that a light, new resonance can affect the low-q 2 bin of R K * only in a very restricted range of parameter space once all relevant constraints are taken into account.…”

On the importance of electroweak corrections for B anomalies

“…The above setup is the most natural one to accommodate simultaneously and in a correlated way charged-and neutral-current anomalies. Moreover, it is favoured by global fit analyses of b → s + − data [16][17][18][19][20][21][22] including the very recent experimental result for R µ/e K * [54][55][56][57][58][59][60][61][62]. At the electroweak scale m EW , additional operators will arise from Lagrangian (2.3), due to the well-known phenomenon of operator mixing.…”

The B → πK puzzle revisited

“…These include (i) R K (LHCb [7]) and (ii) R K * (LHCb [8]), where R K,K * ≡ B(B +,0 → K +, * 0 µ + µ − )/B(B +,0 → K +, * 0 e + e − ), (iii) the angular distribution of B → K * µ + µ − (LHCb [9, 10], Belle [11], ATLAS [12] and CMS [13]), and (iv) the branching fraction and angular distribution of B 0 s → φµ + µ − (LHCb [14,15]). Recent analyses of these discrepancies [16][17][18][19][20][21][22][23][24][25][26] combine constraints from all measurements and come to the following conclusions: (i) there is indeed a significant disagreement with the SM, somewhere in the range of 4-6σ, and (ii) the most probable explanation is that the NP primarily affects b → sµ + µ − transitions. Arguably the simplest NP explanation is that its contribution to b → sµ + µ − comes from the tree-level exchange of a Z boson that has a flavor-changing coupling tosb, and also couples to µ + µ − .…”

“…Following its announcement, a number of papers appeared [16][17][18][19][20][21][22][23][24][25][26] computing the size of the discrepancy with the SM, and determining the general properties of the NP required to explain the results. Combining constraints from all measurements, the general consensus is that there is indeed a significant disagreement with the SM, somewhere in the range of 4-6σ (this large range is due to the fact that different groups deal with the theoretical uncertainties in different ways).…”