Radiative Decays of the P-Wave Charmed Mesons

Minor (mainly numerical) corrections.Comment: 12 pages, LaTeX, MZ-TH/92-5

Helicity fractions of W bosons from top quark decays at NNLO in QCD

Decay rates of unpolarized top quarks into longitudinally and transversally polarized W bosons are calculated to second order in the strong coupling constant alpha_s. Including the finite bottom quark mass and electroweak effects, the Standard Model predictions for the W boson helicity fractions are F_L=0.687(5), F_+=0.0017(1), and F_-=0.311(5).Comment: 5 pages, 1 figur

Semileptonic and nonleptonic decays of Bc

Using our relativistic constituent quark model we present results on the exclusive nonleptonic and semileptonic decays of the Bc-meson. The nonleptonic decays are studied in the framework of the factorization approximation. We calculate the branching ratios for a large set of exclusive nonleptonic and semileptonic decays of the Bc-meson and compare our results with the results of other models.Comment: 4 pages, proceeding of the talk given by Pietro Santorelli at IFAE 2006, Pavia, 19-21 Aprile 200

J/\psi dissociation cross sections in a relativistic quark model

We calculate the amplitudes and the cross sections of the charm dissociation processes J/\psi \pi => D \bar D, D* \bar D, D \bar D*, D* \bar D* within a relativistic constituent quark model. We consistently account for the contributions coming from both the box and triangle diagrams that contribute to the dissociation processes. The cross section is dominated by the D* \bar D and D* \bar D* channels. When summing up the four channels we find a maximum total cross section of about 2.3 mb at sqrt(s) \approx 4.1 GeV. We compare our results to the results of other model calculations.Comment: 22 pages, 9 figures, typos corrected, this version will appear on Phys. Rev.

Semileptonic decays of Bc mesons into charmonium states in a relativistic quark model

We use the framework of a relativistic constituent quark model to study the semileptonic transitions of the Bc meson into CCbar charmonium states where CCbar = etaC (1S0), J/psi (3S1), chiC0 (3P0), chiC1 (3P1), hc (1P1), chiC2 (3P2), psi (3D2). We compute the q^2-dependence of all relevant form factors and give predictions for their semileptonic Bc decay modes including also their tau-modes. We derive a formula for the polar angle distribution of the charged lepton in the (l nu) c.m. frame and compute the partial helicity rates that multiply the angular factors in the decay distribution. For the discovery channel [B_c => J/psi (=> mu+ mu-) l nu] we compute the transverse/longitudinal composition of the J/psi which can be determined by an angular analysis of the decay J/psi => mu+ mu-. We compare our results with the results of other calculations.Comment: 16 pages RevTex, this version will appear in Physical Review