Inclusive Charmed-Baryon Decays and Lifetimes

We have quantitatively reanalyzed the inclusive charmed-baryon decays. New ingredients are the Voloshin preasymptotic effects in semileptonic decays and the Cabibbo-subleading contributions to both semileptonic and nonleptonic decays. It has been found that the Cabbibo-subleading Voloshin contribution essentially improves the theoretical semileptonic branching ratio of $\Lambda_c^{+}$, in agreement with experiment. The semileptonic branching ratios for $\Xi_c^{+}$ and $\Omega_c^{0}$ are found to be large, i.e., of the order of 20%. The lifetimes hierarchy is in a good qualitative and even quantitative agreement with experiment except for the $\Xi_c^{+}$ lifetime, which is somewhat smaller than the experimental value. Future measurements, especially measurements of the semileptonic branching ratios for $\Omega_c^{0}$, $\Xi_c^{+}$ and $\Xi_c^{0}$ should be decisive for the check of this approach.Comment: 13 pages, Latex, 3 figures included, shortened version, to appear in Z.Phys.

QCD Radiative Correction to Zero Recoil Sum Rules for Heavy Flavor Transitions in the Small Velocity Limit.

We consider the small velocity sum rules for heavy flavour semileptonic transitions that are used to estimate the zero recoil values of semileptonic heavy flavour form factors. We analyze the complete O($\alpha _S$) radiative correction to these sum rules. The corrections are universal and influence all "model-independent" bounds previously derived for semileptonic form factors at zero recoil.Comment: 13 pages, LaTeX, 3 figures

Semileptonic BcB_c Decay and Heavy Quark Spin Symmetry

Semileptonic decay of the $B_c$ meson is studied in the heavy quark limit. The six possible form factors for $B_c \rightarrow B_s (B^0),B_s^* (B^{*0})$ semileptonic decay are determined by two invariant functions. Only one of these functions contributes at zero recoil, where it is calculable to lowest order in an operator product expansion in terms of the meson decay constant $f_B$ and the $B_c$ wavefunction. A similar result is found for $B_c \rightarrow D^0,D^{*0}$ and for $B_c\rightarrow\eta_c,J/\psi$ semileptonic decay for a restricted kinematic region. Semileptonic $B_c$ decay provides a means for determining the KM mixing angle $|V_{ub}|$.Comment: (12 Pages, no figures

Heavy Flavour Physics

The current status of the theory and phenomenology of weak decays of hadrons containing a heavy quark is reviewed. Exclusive semileptonic and rare decays of $B$ mesons are discussed, as well as inclusive decay rates, the semileptonic branching ratio of the $B$ meson, and the lifetimes of $b$-flavoured hadrons. Determinations of $\alpha_s$ from $\Upsilon$ spectroscopy are briefly presented.Comment: 27 pages, 7 figures, discussion of the theory of the B semileptonic branching ratio has been revise

Lattice results for D/Ds leptonic and semileptonic decays

This review article summarizes recent lattice QCD results for D and D_s meson leptonic and semileptonic decays. Knowing the meson decay constants and semileptonic form factors from theory, one can extract CKM elements V_cd and V_cs from experimental results. At present, the most accurate results for decay constants are from the Fermilab Lattice and MILC Collaborations: f_D=212.5±0.5_{stat}+0.6−1.5|_{syst} MeV and fDs=248.9±0.2_{stat}+0.5−1.6|_{syst} MeV, giving V_cd=0.2184±0.009_{expt}+0.0008−0.0016|_{lattice} and V_cs=1.017±0.02_{expt}+0.002−0.007|_{lattice}. The shapes of the semileptonic form factors from lattice QCD agree very well with experiment, and the accuracy is currently at the 2-5% level for D→πℓν and 1-2% for D→Kℓν. Extracting the CKM elements from the semileptonic decays yields V_cd=0.225(6)_{expt}(10)_{lattice} (HPQCD Collaboration) and V_cs=0.963(5)_{expt}(14)_{lattice} (HPQCD Collaboration). These lattice calculations also revealed that the semileptonic form factors are insensitive to whether the spectator quark is a light or strange quark

Constraining weak annihilation using semileptonic D decays

The recently measured semileptonic D_s decay rate can be used to constrain weak annihilation (WA) effects in semileptonic D and B decays. We revisit the theoretical predictions for inclusive semileptonic D_{(s)} decays using a variety of quark mass schemes. The most reliable results are obtained if the fits to B decay distributions are used to eliminate the charm quark mass dependence, without using any specific charm mass scheme. Our fit to the available data shows that WA is smaller than commonly assumed. There is no indication that the WA octet contribution (which is better constrained than the singlet contribution) dominates. The results constrain an important source of uncertainty in the extraction of |Vub| from inclusive semileptonic B decays.Comment: 5 pages, 2 figures, published versio