On the Standard Model prediction for $\mathcal{B}(B_{s,d} \to \mu^{+} \mu^{-})$

Abstract

The decay B s → µ + µ − is one of the milestones of the flavor program at the LHC. We reappraise its Standard Model prediction. First, by analyzing the theoretical rate in the light of its main parametric dependence, we highlight the importance of a complete evaluation of higher-order electroweak corrections, at present known only in the large-m t limit, and leaving sizable dependence on the definition of electroweak parameters. Using insights from a complete calculation of such corrections for K → πνν decays, we find a scheme in which NLO electroweak corrections are likely to be negligible. Second, we address the issue of the correspondence between the initial and the final state detected by the experiments, and those used in the theoretical prediction. Particular attention is devoted to the effect of the soft radiation, that has not been discussed for this mode in the previous literature, and that can lead to O(10%) corrections to the decay rate. The "non-radiative" branching ratio (that is equivalent to the branching ratio fully inclusive of bremsstrahlung radiation) is estimated to be (3.23 ± 0.27) × 10 −9 for the flavor eigenstate, with the main uncertainty resulting from the value of f Bs , followed by the uncertainty due to higher order electroweak corrections. Applying the same strategy to B d → µ + µ − , we find for its non-radiative branching ratio (1.07 ± 0.10) × 10 −10 .

Updated constraints on general squark flavor mixing

“…The present experimental value for this observable [38,39] and the prediction within the SM [40] are given by…”

Cornering light neutralino dark matter at the LHC

“…Although the situation is not conclusive yet (the above claims are not consistent with the XENON100 results [27] and do not even seem to be perfectly compatible with each other [53,54,55]), the above results might be broadly accounted for by a light WIMP with a mass in the range of O (10) GeV and a spin-independent (SI) elastic DM-nucleon cross-section, σ SI , of the order of 10 −42 to 10 −40 cm 2 . As previously mentioned, it is not possible to realize the above configuration within the MSSM [23,24,22]: in fact, such a relatively large spinindependent cross-sections require a light extended Higgs sector, which is now excluded for moderate to large tan β by (i) searches at the LHC for extra Higgs bosons decaying into pairs of taus [25,26], and (ii) the recent observation of the decay B s → µ + µ − at LHCb [28] with a branching fraction compatible with the SM prediction [56].…”

Measurement of theBs0→μ+μ−Branching Fraction and Search forB0→Aaij1, Adeva2, Adinolfi3 et al. 2013Phys. Rev. Lett.347192380View full textAdd to dashboardCite

“…These theoretical predictions are for decays at decay time t ¼ 0, and have been updated with respect to Refs. [1,2] using the latest average for the B 0 s meson lifetime, B 0 s ¼ 1:516 AE 0:011 ps [3]. The uncertainty is dominated by the precision of lattice QCD calculations of the decay constants [1,[4][5][6][7].…”

“…[1,2] using the latest average for the B 0 s meson lifetime, B 0 s ¼ 1:516 AE 0:011 ps [3]. The uncertainty is dominated by the precision of lattice QCD calculations of the decay constants [1,[4][5][6][7]. In the B 0 s system, due to the finite width difference, the comparison between the above prediction and the measured time-integrated branching fraction requires a model-dependent correction [8].…”