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Register a new user$B to K ell^{+}ell^{-}$ decay at large hadronic recoil
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We predict the amplitude of the $Bto K ell^+ell^-$ decay in the region of the dilepton invariant mass squared $0<q^2leq m_{J/psi}^2$, that is, at large hadronic recoil. The $Bto K$ form factors entering the factorizable part of the decay amplitude are obtained from QCD light-cone sum rules. The nonlocal effects, generated by the four-quark and penguin operators combined with the electromagnetic interaction, are calculated at $q^2<0$, far below the hadronic thresholds. For hard-gluon contributions we employ the QCD factorization approach. The soft-gluon nonfactorizable contributions are estimated from QCD light-cone sum rules. The result of the calculation is matched to the hadronic dispersion relation in the variable $q^2$, which is then continued to the kinematical region of the decay. The overall effect of nonlocal contributions in $Bto Kell^+ell^-$ at large hadronic recoil is moderate. The main uncertainty of the predicted $Bto K ell^+ell^-$ partial width is caused by the $Bto K$ form factors. Furthermore, the isospin asymmetry in this decay is expected to be very small. We investigate the deviation of the observables from the Standard Model predictions by introducing a generic new physics contribution to the effective Hamiltonian.
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We study the rare decay $Bto K_2^ast(1430)(to Kpi)ell^+ell^-$ in the Standard Model and beyond. Working in the transversity basis, we exploit the relations between the heavy-to-light form factors in the limit of heavy quark ($m_bto infty$) and large energy ($E_{K_2^ast}to infty$) of the $K^ast_2$ meson. This allows us to construct observables where at leading order in $Lambda_{rm QCD}/m_b$ and $alpha_s$ the form factor dependence involving the $Bto K^ast_2$ transitions cancels. Higher order corrections are systematically incorporated in the numerical analysis. In the Standard Model the decay has a sizable branching ratio and therefore a large number of events can be expected at LHCb. Going beyond the Standard Model, we explore the implications of the global fit to presently available $bto sell^+ell^-$ data on the $Bto K_2^ast ell^+ell^-$ observables.
We calculate the amplitude of the rare flavour-changing neutral-current decay $Bto piell^+ell^-$ at large recoil of the pion. The nonlocal contributions in which the weak effective operators are combined with the electromagnetic lepton-pair emission are systematically taken into account. These amplitudes are calculated at off-shell values of the lepton-pair mass squared, $q^2<0$, employing the operator-product expansion, QCD factorization and light-cone sum rules. The results are fitted to hadronic dispersion relations in $q^2$, including the intermediate vector meson contributions. The dispersion relations are then used in the physical region $q^2>0$. Our main result is the process-dependent addition $Delta C^{(Bpi)}_9(q^2)$ to the Wilson coefficient $C_9$ obtained at $4m_ell^2<q^2lesssim m_{J/psi}^2$. Together with the $Bto pi$ form factors from light-cone sum rules, this quantity is used to predict the differential rate, direct CP-asymmetry and isospin asymmetry in $Bto piell^+ell^-$. We also estimate the total rate of the rare decay $Bto pi ubar{ u}$.
In this paper we present a detailed study of the four-body decay $B^0to K^{+}pi^{-}ell^{+}ell^{-}$, where tensions with the Standard Model predictions have been observed. Our analysis of the decay with P- and S-wave contributions to the $K^{+}pi^{-}$ system develops a complete understanding of the symmetries of the distribution, in the case of massless and massive leptons. In both cases, the symmetries determine relations between the observables in the $B^0to K^{+}pi^{-}ell^{+}ell^{-}$ decay distribution. This enables us to define the complete set of observables accessible to experiments, including several that have not previously been identified. The new observables arise when the decay rate is written differentially with respect to $m_{Kpi}$. We demonstrate that experiments will be able to fit this full decay distribution with currently available data sets and investigate the sensitivity to new physics scenarios given the experimental precision that is expected in the future. The symmetry relations provide a unique handle to explore the behaviour of S-wave observables by expressing them in terms of P-wave observables, therefore minimising the dependence on poorly-known S-wave form factors. Using this approach, we construct two theoretically clean S-wave observables and explore their sensitivity to new physics. By further exploiting the symmetry relations, we obtain the first bounds on the S-wave observables using two different methods and highlight how these relations may be used as cross-checks of the experimental methodology. We identify a zero-crossing point that would be at a common dilepton invariant mass for a subset of P- and S-wave observables, and explore the information on new physics and hadronic effects that this zero point can provide.
The present status of the LHC anomalies found in exclusive semileptonic $bto sell^+ell^-$ decays is discussed with special emphasis on the exclusive 4-body angular distribution $B to K^*(to Kpi)ell^+ell^-$. The treatment of hadronic uncertainties in this mode is briefly reviewed, and some of the analyses in the literature are critically reassessed. The global picture provided by the global fit points to a coherent pattern of deviations with a significance substantially above 4$sigma$ for different New Physics scenarios. Finally, we propose as the next step in the field to focus on the study of optimized observables that compare electron and muon modes, sensitive to lepton-flavour universality violations and free from hadronic uncertainties (including charm) in the SM, the so called $Q_i$ observables.
Ratios of branching fractions of semileptonic B decays, $(B to H mu mu)$ over $(B to H ee)$ with $H=K, K^*,X_s, K_0(1430), phi, ldots$ are sensitive probes of lepton universality. In the Standard Model, the underlying flavor changing neutral current process $brightarrow s ell ell$ is lepton flavor universal. However models with new flavor violating physics above the weak scale can give substantial non-universal contributions. The leading contributions from such new physics can be parametrized by effective dimension six operators involving left- or right-handed quarks. We show that in the double ratios $R_{X_s}/R_K$, $R_{K^*}/R_K$ and $R_phi/R_K$ the dependence on new physics coupling to left-handed quarks cancels out. Thus a measurement of any of these double ratios is a clean probe of flavor nonuniversal physics coupling to right-handed quarks. We also point out that the observables $R_{X_s}$, $R_{K^*}$, $R_{K_0(1430)}$ and $R_phi$ depend on the same combination of Wilson coefficients and therefore satisfy simple consistency relations.
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