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Register a new userOn Exclusive $h to V ell^+ ell^-$ Decays
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We study a set of exclusive decay modes of the Standard Model Higgs boson into a vector meson and a dilepton pair: $hto V ell^+ ell^-$, with $V=Upsilon, J/psi,phi$, and $ell=mu, tau$, determining the decay rates, the dilepton mass spectra and the $V$ longitudinal helicity fraction distributions. In the same framework, we analyze the exclusive modes into neutrino pairs $hto V u bar u$. We also discuss the implications of the recent CMS and ATLAS results for the lepton flavor-changing process $hto tau^+ mu^-$ on the $hto V tau^+ mu^-$ decay modes.
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This article analyses the available inputs in $btopilnu$ and $btorholnu$ decays which include the measured values of differential rate in different $q^2$-bins (lepton invariant mass spectrum), lattice, and the newly available inputs on the relevant form-factors from the light-cone sum rules (LCSR) approach. We define different fit scenarios, and in each of these scenarios, we predict a few observables in the standard model (SM). For example, $R(M) =frac{mathcal{B}(B to Mell_i u_{ell_i})}{mathcal{B}(Bto Mell_j u_{ell_j})} $, $R^{ell_i}_{ell_j}(M) =frac{mathcal{B}(Bto ell_i u_{ell_i})}{mathcal{B}(B to Mell_j u_{ell_j})}$ with M = $pi$ or $rho$ and $ell_{i,j} = e, mu$ or $tau$. We also discuss the new physics (NP) sensitivities of all these observables and obtain bounds on a few NP Wilson coefficients in $bto u tau u_{tau}$ decays using the available data. We have noted that the data at present allows sizeable NP contributions in this mode. Also, we have predicted a few angular observables relevant to these decay modes.
We discuss the general properties of the amplitude of the $Bto l^+l^-l u$ decays and calculate the related kinematical distributions $d^2Gamma/dq^2dq^2$, $q$ the momentum of the $l^+l^-$ pair emitted from the electromagnetic vertex and $q$ the momentum of the $l u$ pair emitted from the weak vertex. We emphasize that electromagnetic gauge invariance imposes essential constraints on the $Bto gamma^*l u$ amplitude at small $q^2$ which in the end yield the behaviour of the differential branching fraction as $dGamma(Bto l^+l^-l u)/dq^2propto 1/q^2$ and a mild logarithmic dependence of $Gamma(Bto l^{+}l^{-}l u)$ on the lepton mass $m_l$. Consequently, (i) the main contribution to the decay rate $Gamma(Bto mu^+mu^-e u_e )$ comes from the region of light vector resonances $rho^0$ and $omega$, $q^2simeq M_rho^2, M_omega^2$ and (ii) the decay rate $Gamma(Bto e^{+}e^{-}mu u_mu)$ receives comparable contributions from the region of small $q^2$ and from the resonance region. As the result, the decay rate $Gamma(Bto e^+e^-mu u_mu)$ is only a factor $sim 2$ larger than $Gamma(Bto mu^+mu^-e u_e)$. We perform a detailed analysis of the uncertainties in the theoretical predictions for the decays $Bto l^+l^-l u$ in the Standard Model. We found that the theoretical expectations for such decays in the Standard Model are only marginally compatible with the recent upper limits of the LHCb collaboration.
We present the prospects of an angular analysis of the $Lambda_b to Lambda(1520)ell^+ell^-$ decay. Using the expected yield in the current dataset collected at the LHCb experiment, as well as the foreseen ones after the LHCb upgrades, sensitivity studies are presented to determine the experimental precision on angular observables related to the lepton distribution and their potential to identify New Physics. The forward-backward lepton asymmetry at low dilepton invariant mass is particularly promising. NP scenarios favoured by the current anomalies in $bto sell^+ell^-$ decays can be distinguished from the SM case with the data collected between the Run 3 and the Upgrade 2 of the LHCb experiment.
Recent results obtained in experiments at the LHC in the field of rare $b$-hadron decays are reviewed in this contribution, with a focus on $bto qellell$ processes. A general status is presented as well as recently completed measurements.
We calculate tree-level contributions to the inclusive rare $bar B to X_{s(d)} , ell^+ell^-$ decays. At the partonic level they stem from the five-particle process $b to s(d) , q bar q , ell^+ell^-$, with $q in {u,d,s}$. While for $b to d$ transitions such five-body final states contribute at the same order in the Wolfenstein expansion compared to the three-body partonic decay, they are CKM suppressed in $b to s$ decays. In the perturbative expansion, we include all leading-order contributions, as well as partial next-to-leading order QCD and QED effects. In the case of the differential branching ratio, we present all results completely analytically in terms of polylogarithmic functions of at most weight three. We also consider the differential forward-backward asymmetry, where all except one interference could be obtained analytically. From a phenomenological point of view the newly calculated contributions are at the percent level or below.
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