Soft-gluon effects in semileptonic decays of charmed F mesons

The QCD multipole expansion is applied to the study of nonperturbative soft-gluon effects in semileptonic decays of charmed F mesons. For reasonable values of F-meson bound-state parameters, the soft-gluon effects activate quark-annihilation processes, leading to a significant enhancement of semileptonic decay rates.     

Bag models and semileptonic decays

Starting from different versions of the bag model, we compute the different amplitudes relevant for weak interaction transition elements in semileptonic decays. It seems that such models might be quite accurate in describing observations.     

Helicity analysis of semileptonic hyperon decays including lepton-mass effects

Using the helicity method we derive complete formulas for the joint angular decay distributions occurring in semileptonic hyperon decays including lepton-mass and polarization effects. Compared to the traditional covariant calculation, the helicity method allows one to organize the calculation of the angular decay distributions in a very compact and efficient way. In the helicity method the angular analysis is of cascade type, i.e. each decay in the decay chain is analyzed in the respective rest system of that particle. Such an approach is ideally suited as input for a Monte Carlo event generation program. As a specific example we take the decay  (l ⁻=e ⁻,μ ⁻) followed by the nonleptonic decay Σ ⁺→p+π ⁰ for which we show a few examples of decay distributions which are generated from a Monte Carlo program based on the formulas presented in this paper. All the results of this paper are also applicable to the semileptonic and nonleptonic decays of ground-state charm and bottom baryons, and to the decays of the top quark.     

Exclusive semileptonic heavy meson decays including lepton mass effects

We discuss the exclusive semi-leptonic (s.l.) bottom meson decaysB→D(D ^*)+l+v where we include non-zero lepton mass effects in the kinematics and dynamics. We develop the general formalism for the non-zero lepton mass case. We then look at how rates, spectra and angular correlations are affected by non-zero lepton masses in the context of a specific spectator quark model. Numerical results are presented for s.l. decays involving thee-, μ- and τ-leptons. We also discuss the s.l. decaysB→π(ρ),D→K(K ^*) and the free quark decay model.     

Semileptonic b-->u decays: lepton invariant mass spectrum

We compute O(alpha(2)(s)) QCD corrections to the lepton invariant mass spectrum in the decay b-->ulnu(l), relevant for the determination of the Cabibbo-Kobayashi-Maskawa matrix element /V(ub)/. Our method can also be used to evaluate moments of the lepton energy distribution with an O(alpha(2)(s)) accuracy. The Abelian part of our result gives the neutrino invariant mass spectrum in the muon decay and, upon integration, the O(alpha(2)) correction to the muon lifetime.