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Register a new userHunting for $B^+to K^+ tau^+tau^-$ imprints on the $B^+ to K^+ mu^+mu^-$ dimuon spectrum
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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.
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We evaluate long-distance electromagnetic (QED) contributions to $bar{B}{}^0 to D^+ tau^{-} bar{ u}_{tau}$ and $B^- to D^0 tau^{-} bar{ u}_{tau}$ relative to $bar{B}{}^0 to D^+ mu^{-} bar{ u}_{mu}$ and $B^- to D^0 mu^{-} bar{ u}_{mu}$, respectively, in the standard model. We point out that the QED corrections to the ratios $R(D^{+})$ and $R(D^{0})$ are not negligible, contrary to the expectation that radiative corrections are almost canceled out in the ratio of the two branching fractions. The reason is that long-distance QED corrections depend on the masses and relative velocities of the daughter particles. We find that theoretical predictions for $R(D^{+})^{tau/mu}$ and $R(D^{0})^{tau/mu}$ can be amplified by $sim4%$ and $sim3%$, respectively, for the soft-photon energy cut in range $20$-$40$ MeV.
We perform an analysis within the Standard Model of $B^{0,+} to K^{*0,+} mu^+ mu^-$ decays in light of the recent measurements from the LHCb experiment, showing that new data strengthen the need for sizable hadronic contributions and correlations among them. We then extend our analysis to New Physics via the Standard Model Effective Theory, and carry out a state-of-the-art fit of available $b to s ell^+ ell^-$ data, including possible hadronic contributions. We find the case of a fully left-handed operator standing out as the simplest scenario with a significance of almost $6sigma$.
We analyse the results recently presented on the $B^{+} to K^{*+} mu^+ mu^-$ angular observables by the LHCb Collaboration which show indications for New Physics beyond the Standard Model. Within a model-independent analysis, we compare the fit results with the corresponding results for the angular observables in $B^{0} to K^{*0} mu^+ mu^-$.
A search is performed for the lepton number violating decay $B^{+}to h^- mu^+ mu^+$, where $h^-$ represents a $K^-$ or a $pi^-$, using data from the LHCb detector corresponding to an integrated luminosity of $36pb^{-1}$. The decay is forbidden in the Standard Model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of $B(B^{+} to K^- mu^+ mu^+) < 5.4times 10^{-8}$ and $B(B^{+} to pi^- mu^+ mu^+) < 5.8times 10^{-8}$ are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.
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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