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Register a new userNew Physics in $b to s mu^+ mu^-$ after the Measurement of $R_{K^*}$
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The recent measurement of $R_{K^*}$ is yet another hint of new physics (NP), and supports the idea that it is present in $bto smu^+mu^-$ decays. We perform a combined model-independent and model-dependent analysis in order to deduce properties of this NP. Like others, we find that the NP must obey one of two scenarios: (I) $C_9^{mumu}({rm NP}) < 0$ or (II) $C_9^{mumu}({rm NP}) = - C_{10}^{mumu}({rm NP}) < 0$. A third scenario, (III) $C_9^{mumu}({rm NP}) = - C_{9}^{prime mumu}({rm NP})$, is rejected largely because it predicts $R_K = 1$, in disagreement with experiment. The simplest NP models involve the tree-level exchange of a leptoquark (LQ) or a $Z$ boson. We show that scenario (II) can arise in LQ or $Z$ models, but scenario (I) is only possible with a $Z$. Fits to $Z$ models must take into account the additional constraints from $B^0_s$-${bar B}^0_s$ mixing and neutrino trident production. Although the LQs must be heavy, O(TeV), we find that the $Z$ can be light, e.g., $M_{Z} = 10$ GeV or 200 MeV.
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At present, there are several measurements of $B$ decays that exhibit discrepancies with the predictions of the SM, and suggest the presence of new physics (NP) in $b to s mu^+ mu^-$ transitions. Many NP models have been proposed as explanations. These involve the tree-level exchange of a leptoquark (LQ) or a flavor-changing $Z$ boson. In this paper we examine whether it is possible to distinguish the various models via CP-violating effects in $B to K^{(*)} mu^+ mu^-$. Using fits to the data, we find the following results. Of all possible LQ models, only three can explain the data, and these are all equivalent as far as $b to s mu^+ mu^-$ processes are concerned. In this single LQ model, the weak phase of the coupling can be large, leading to some sizeable CP asymmetries in $B to K^{(*)} mu^+ mu^-$. There is a spectrum of $Z$ models; the key parameter is $g_L^{mumu}$, which describes the strength of the $Z$ coupling to $mu^+mu^-$. If $g_L^{mumu}$ is small (large), the constraints from $B^0_s$-${bar B}^0_s$ mixing are stringent (weak), leading to a small (large) value of the NP weak phase, and corresponding small (large) CP asymmetries. We therefore find that the measurement of CP-violating asymmetries in $B to K^{(*)} mu^+ mu^-$ can indeed distinguish among NP $b to s mu^+ mu^-$ models
This talk discusses possible new physics interpretations of recent experimental results on the B-->K*mu+mu- decay that show a discrepancy with the Standard Model predictions. A model independent analysis that takes into account all the relevant observables in B-->K*mu+mu- and in related b-->s transitions allows to identify a consistent new physics explanation of the discrepancy. An explicit realization in the context of a Z model is presented. The model is based on the U(1) gauge group associated with the difference between muon- and tau-lepton number, L_mu - L_tau.
One of the main indications for New Physics in rare $B$-decays is deduced from the tension between experimental and Standard Model predictions of the angular analysis of the $B^0 to K^{*0} mu^+mu^-$ decay. There are however possible non-local hadronic effects which in principle can also explain these tensions. In this work, we consider a statistical approach for differentiating the source of the tension in $B^0 to K^{*0} mu^+mu^-$ observables and we also investigate the prospects of such a comparison with future data from the LHCb experiment.
We investigate the possibility of indirectly constraining the $B^{+}to K^{+}tau^+tau^-$ decay rate using precise data on the $B^{+}to K^{+}mu^+mu^-$ dimuon spectrum. To this end, we estimate the distortion of the spectrum induced by the $B^{+}to K^{+}tau^+tau^-to K^{+} mu^+mu^-$ re-scattering process, and propose a method to simultaneously constrain this (non-standard) contribution and the long-distance effects associated to hadronic intermediate states. The latter are constrained using the analytic properties of the amplitude combined with data and perturbative calculations. Finally, we estimate the sensitivity expected at the LHCb experiment with present and future datasets. We find that constraints on the branching fraction of $O(10^{-3})$, competitive with current direct bounds, can be achieved with the current dataset, while bounds of $O(10^{-4})$ could be obtained with the LHCb upgrade-II luminosity.
The new angular analysis of the decay $B to K^* ell^+ ell^-$ recently presented by the LHCb Collaboration still indicates some tensions with the Standard Model predictions. There are several ongoing analyses to solve the problem of separating hadronic and New Physics effects in this decay, but the significance of the observed tensions in the angular observables in $B to K^* mu^+mu^-$ is still dependent on a theory guesstimate of the hadronic contributions to these decays. Using the new data from LHCb we offer two tests which make a statistical comparison to determine whether the most favoured explanation of the anomalies is New Physics or underestimated hadronic effects. We then analyse the usefulness of these tests in two future scenarios. Finally, we update our global fits to all available $b to s $ data and discuss the impact of the new LHCb measurements.
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