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Register a new userRadiative and Semileptonic B Decays Involving Higher K-Resonances in the Final States
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We study the radiative and semileptonic B decays involving a spin-$J$ resonant $K_J^{(*)}$ with parity $(-1)^J$ for $K_J^*$ and $(-1)^{J+1}$ for $K_J$ in the final state. Using the large energy effective theory (LEET) techniques, we formulate $B to K_J^{(*)}$ transition form factors in the large recoil region in terms of two independent LEET functions $zeta_perp^{K_J^{(*)}}$ and $zeta_parallel^{K_J^{(*)}}$, the values of which at zero momentum transfer are estimated in the BSW model. According to the QCD counting rules, $zeta_{perp,parallel}^{K_J^{(*)}}$ exhibit a dipole dependence in $q^2$. We predict the decay rates for $B to K_J^{(*)} gamma$, $B to K_J^{(*)} ell^+ ell^-$ and $B to K_J^{(*)} u bar{ u}$. The branching fractions for these decays with higher $K$-resonances in the final state are suppressed due to the smaller phase spaces and the smaller values of $zeta^{K_J^{(*)}}_{perp,parallel}$. Furthermore, if the spin of $K_J^{(*)}$ becomes larger, the branching fractions will be further suppressed due to the smaller Clebsch-Gordan coefficients defined by the polarization tensors of the $K_J^{(*)}$. We also calculate the forward backward asymmetry of the $B to K_J^{(*)} ell^+ ell^-$ decay, for which the zero is highly insensitive to the $K$-resonances in the LEET parametrization.
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Two of the elements of the Cabibbo-Kobayashi-Maskawa quark mixing matrix, $|V_{ub}|$ and $|V_{cb}|$, are extracted from semileptonic B decays. The results of the B factories, analysed in the light of the most recent theoretical calculations, remain puzzling, because for both $|V_{ub}|$ and $|V_{cb}|$ the exclusive and inclusive determinations are in clear tension. Further, measurements in the $tau$ channels at Belle, Babar, and LHCb show discrepancies with the Standard Model predictions, pointing to a possible violation of lepton flavor universality. LHCb and Belle II have the potential to resolve these issues in the next few years. This article summarizes the discussions and results obtained at the MITP workshop held on April 9--13, 2018, in Mainz, Germany, with the goal to develop a medium-term strategy of analyses and calculations aimed at solving the puzzles. Lattice and continuum theorists working together with experimentalists have discussed how to reshape the semileptonic analyses in view of the much higher luminosity expected at Belle II, searching for ways to systematically validate the theoretical predictions in both exclusive and inclusive B decays, and to exploit the rich possibilities at LHCb.
We review some recent progress in the theory of electroweak radiative corrections in semileptonic decay processes. The resurrection of the so-called Sirlins representation based on current algebra relations permits a clear separation between the perturbatively-calculable and incalculable pieces in the $mathcal{O}(G_Falpha)$ radiative corrections. The latter are expressed as compact hadronic matrix elements that allow systematic non-perturbative analysis such as dispersion relation and lattice QCD. This brings substantial improvements to the precision of the electroweak radiative corrections in semileptonic decays of pion, kaon, free neutron and $J^P=0^+$ nuclei that are important theory inputs in precision tests of the Standard Model. Unresolved issues and future prospects are discussed.
We evaluate the non-resonant decay amplitude of the process $B^pmto K^pmpi^+ pi^-$ using an approach based on final state hadronic interactions described in terms of meson exchanges. We conclude that this mechanism generates inhomogeneities in the Dalitz plot of the B decay.
With the advent of the LHC, we will be able to probe New Physics (NP) up to energy scales almost one order of magnitude larger than it has been possible with present accelerator facilities. While direct detection of new particles will be the main avenue to establish the presence of NP at the LHC, indirect searches will provide precious complementary information, since most probably it will not be possible to measure the full spectrum of new particles and their couplings through direct production. In particular, precision measurements and computations in the realm of flavour physics are expected to play a key role in constraining the unknown parameters of the Lagrangian of any NP model emerging from direct searches at the LHC. The aim of Working Group 2 was twofold: on one hand, to provide a coherent, up-to-date picture of the status of flavour physics before the start of the LHC; on the other hand, to initiate activities on the path towards integrating information on NP from high-pT and flavour data.
We consider leptonic $B^-to ell^- bar u_ell$ and semileptonic $bar B to pi ell^- bar u_ell$, $bar B to rho ell^- bar u_ell$ decays and present a strategy to determine short-distance coefficients of New-Physics operators and the CKM element $|V_{ub}|$. As the leptonic channels play a central role, we illustrate this method for (pseudo)-scalar operators which may lift the helicity suppression of the corresponding transition amplitudes arising in the Standard Model. Utilising a new result by the Belle collaboration for the branching ratio of $B^-to mu^- bar u_mu$, we explore theoretically clean constraints and correlations between New Physics coefficients for leptonic final states with $mu$ and $tau$ leptons. In order to obtain stronger bounds and to extract $|V_{ub}|$, we employ semileptonic $bar B to pi ell^- bar u_ell$ and $bar B to rho ell^- bar u_ell$ decays as an additional ingredient, involving hadronic form factors which are determined through QCD sum rule and lattice calculations. In addition to a detailed analysis of the constraints on the New Physics contributions following from current data, we make predictions for yet unmeasured decay observables, compare them with experimental constraints and discuss the impact of CP-violating phases of the New-Physics coefficients.
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