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Register a new userExperimental study for leptonic and semileptonic decays in the charm sector
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S. F. Zhang
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Leptonic and semileptonic decays in the charm sector have been well studied in recent years. With the largest data sample near $Dbar D$ threshold, precision measurements of leptonic and semileptonic decays of charm meson and baryon are perfromed at BESIII. Test for letpon flavor universality is also performed. Sensitivity for rare leptonic and semileptonic charm decays is significantly improved taking advantage of the huge statistics in LHCb and the $B$ factories.
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We review recent experimental progress in the domain of rare radiative, semileptonic and leptonic B decays. The statistical precision attained for these decays has reached a level where they start to impose meaningful constraints on the Cabibbo-Kobayashi-Maskawa matrix, which are complementary to those obtained from hadronic decays. While the current data indicate no deviations from Standard Model predictions, there is still some room for new physics in these decays.
Indirect searches, and in particular rare decays, have proven to be a fruitful field to search for New Physics beyond the Standard Model. While the down-quark sector (B and K) have been studied in detail, less attention was devoted to charm decays due to the smaller expected values and higher theoretical uncertainties of their observables. Recently a renewed interest is growing in rare charm searches. In this article we review the current experimental status of searches for rare decays in charmed hadrons. While the Standard Model rates are yet to be reached, current experimental limits are already putting constraints on New Physics models.
We review recent experimental and theoretical developments in inclusive semileptonic B -> Xc l nu decays. In particular, we discuss the determination of |Vcb| and of the heavy quark masses through fits based on the Operator Product Expansion.
A summary of WG II of the CKM 2018 conference on semileptonic and leptonic $b$-hadron decays is presented. This includes discussions on the CKM matrix element magitudes $|V_{ub}|$ and $|V_{cb}|$, lepton universality tests such as $R(D^{*})$ and leptonic decays. As is usual for semileptonic and leptonic decays, much discussion is devoted towards the interplay between theoretical QCD calculations and the experimental measurements.
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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