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 , in agreement with experiment. The semileptonic branching ratios for and 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 lifetime, which is somewhat smaller than the experimental value. Future measurements, especially measurements of the semileptonic branching ratios for , and should be decisive for the check of this approach. Received: 29 April 1997 / Revised version: 25 June 1997 / Published online: 20 February 1998     

Semileptonic decays of heavy quarks in quantum chromodynamics

We investigate the semileptonic decays of heavy quarks in the leading non-trivial order in quantum chromodynamics. Effects of gluon corrections and the initial quark Fermi motion on the semileptonic rates and decay distributions are calculated. The resulting lepton energy spectrum for the charm semileptonic decay is compared with data to extract the mass of the charm quark. This is combined with the semileptonic branching ratio to predict the charm-quark lifetime. We find the lepton energy spectrum very stable with respect to gluon corrections. Expected spectra from the semileptonic decays of bottom and top quarks are presented. We also study the semileptonic decay process Q → q?v_? + G, involving the emission of a single hard non-collinear gluon. This process should be observable with a branching ratio of a few percent in the decays of top (and heavier) quarks.     

Weak Decays of D and Ds Mesons in a Relativistic Quark Model

The transitions of D and D_s, mesons to light vector states are studied in a relativistic constituent quark model based on the Bethe-Salpeter formalism. The form factors are calculated, and the branching fractions for both semileptonic and nonleptonic decays are given. The results show that the form factors for these transitions deviate substantie from the request of heavy quark symmetry. All the branching ratios for D and D_s semileptonic decays are found to be consistent with data, whereas the calculations of nonleptonic D and D_s decays under the factorization assumption do not agree with experiments. This confirms the conjecture that the factorization scheme is much less applicable in D and D_s decays than in B and B_s decays.     

Rare semileptonic decays of heavy mesons in the heavy quark limit

We study the branching ratios of D+→D0e+ν,DS+→D0e+ν,BS0→B+e-ν,DS+→D+e-e+ and BS0→B0e-e+ rare semileptonic decay processes,which are induced by decays of light quarks,the heavy quarks remain unchanged.The branching ratios of these decay processes are estimated in the heavy quark limit and with SU(3) flavor symmetry.We find that the decay rates are very tiny in the framework of the Standard Model.We also estimate the sensitivities of the measurements of these rare decays at the future experiments,such as BES-Ⅲ,super-B and LHC-b.Observations of these decays may shed some light on new physics beyond the standard model.     

Measurement of the Cabibbo-Kobayashi-Maskawa matrix element V(ub) with B-->rhoenu decays

We present a measurement of the branching fraction for the rare decays B-->rhoenu and extract a value for the magnitude of V(ub), one of the smallest elements of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. The results are given for five different calculations of form factors used to para-metrize the hadronic current in semileptonic decays. Using a sample of 55 x 10(6) BB meson pairs recorded with the BABAR detector at the PEP-II e(+)e(-) storage ring, we obtain B(B0-->rho(-)e(+)nu)=(3.29+/-0.42+/-0.47+/-0.55) x 10(-4) and |V(ub)|=(3.64+/-0.22+/-0.25(+0.39)(-0.56)) x 10(-3), where the uncertainties are statistical, systematic, and theoretical, respectively.     

B → Ds(*) η (') Decays in Perturbative QCD

In this paper, we calculate the branching ratios for B⁺ → D_s⁺η, B⁺ → D_s⁺η ', B⁺ → D_s^*+η, and B⁺ → D_s^*+η ' decays by employing the perturbative QCD (pQCD) factorization approach. Under the two kinds of η-η' mixingschemes, the quark-flavor mixing scheme and the singlet-octet mixingscheme, we find that the calculated branching ratios agree well withthe currently available experimental upper limits. We also consider the so called ``f_{D_s} puzzle', by using two groups of parameters about the D^(*)_s meson decay constants, that are f_{D_s}=241 MeV, f_{D^*_s}=272 MeV and f_{^D_s=}274 MeV, f_{D^*_s}=312 MeV, to calculate the branching ratios for theconsidered decays. We find that the results change 30% by usingthese two different kinds of paramters.     

Observation of the semileptonic decays B-->D*tau-nutau and evidence for B-->Dtau-nutau

We present measurements of the semileptonic decays B--->D0tau-nutau, B--->D*0tau-nutau, B0-->D+tau-nutau, and B0-->D*+tau-nutau, which are potentially sensitive to non-standard model amplitudes. The data sample comprises 232x10(6) Upsilon(4S)-->BB decays collected with the BABAR detector. From a combined fit to B- and B0 channels, we obtain the branching fractions B(B-->Dtau-nutau)=(0.86+/-0.24+/-0.11+/-0.06)% and B(B-->D*tau-nutau)=(1.62+/-0.31+/-0.10+/-0.05)% (normalized for the B0), where the uncertainties are statistical, systematic, and normalization-mode-related.     

Determination of {\rm |V_{ub}|} from the measurement of the inclusive charmless semileptonic branching ratio of b hadrons

From a study of the kinematic properties of the final state produced in the semileptonic decays , the inclusive charmless semileptonic branching ratio of b hadrons is measured. With a sample of 3.6 million hadronic Z decays recorded between 1992 and 1995 with the ALEPH detector at LEP, the value is determined to be , where represents any charmless hadronic state and b is a mixture of b hadrons weighted by their production rates. This measurement yields the result where the last error comes from the conversion of the branching ratio to the CKM matrix element squared. Received: 6 May 1998 / Published online: 14 December 1998     

Further Analysis of Di-gluon Fusion Mechanismfor the Decays of B→Kη′

Di-gluon fusion mechanism might account for the large branching ratios of B→Kη′. But because we know little about the effective η′ɡɡ vertex, there are large uncertainties in perturbative QCD estimations. In this paper, we try several kinds of η′ɡɡ form factors and compare the numerical results with the experiment. We find that, though we know little about η′ɡɡ form factor, if di-gluon fusion mechanism is important in B→Kη′, the branching ratios of the decays B→K^*η′ would be around 10^－5 which can be tested by future experiments.     

Semileptonic decays of baryons in a relativistic quark model

We calculate semileptonic decays of light and heavy baryons in a relativistically covariant constituent quark model. The model is based on the Bethe-Salpeter equation in instantaneous approximation. It generates satisfactory mass spectra for mesons and baryons up to the highest observable energies. Without introducing additional free parameters we compute on this basis helicity amplitudes of electronic and muonic semileptonic decays of baryons. We thus obtain form factor ratios and decay rates in good agreement with experiment.     

Determination of |Vub| from measurements of the electron and neutrino momenta in inclusive semileptonic B decays

We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element |Vub| based on the analysis of semileptonic B decays from a sample of 88 x 10(6) Gamma(4S) decays collected with the BABAR detector at the SLAC PEP-II e+e- storage ring. Charmless semileptonic B decays are selected using measurements of the electron energy and the invariant mass squared of the electron-neutrino pair. We obtain |Vub| =(3.95 +/- 0.26(+0.58)(-0.42) +/- 0.25) x 10(-3), where the errors represent experimental uncertainties, heavy quark parameter uncertainties, and theoretical uncertainties, respectively.     

A new approach to a global fit of the CKM matrix

We report on a new approach to a global CKM matrix analysis taking into account most recent experimental and theoretical results. The statistical framework (Rfit) developed in this paper advocates frequentist statistics. Other approaches, such as Bayesian statistics or the 95% CL scan method are also discussed. We emphasize the distinction of a model testing and a model dependent, metrological phase in which the various parameters of the theory are estimated. Measurements and theoretical parameters entering the global fit are thoroughly discussed, in particular with respect to their theoretical uncertainties. Graphical results for confidence levels are drawn in various one and two-dimensional parameter spaces. Numerical results are provided for all relevant CKM parameterizations, the CKM elements and theoretical input parameters. Predictions for branching ratios of rare K and B meson decays are obtained. A simple, predictive SUSY extension of the Standard Model is discussed. Received: 18 April 2001 / Published online: 10 August 2001     

Standard model Higgs-boson branching ratios with uncertainties

We present an update of the branching ratios for Higgs-boson decays in the Standard Model. We list results for all relevant branching ratios together with corresponding uncertainties resulting from input parameters and missing higher-order corrections. As sources of parametric uncertainties we include the masses of the charm, bottom, and top quarks as well as the QCD coupling constant. We compare our results with other predictions in the literature.     

Weak form factors for semileptonic octet baryon decays in the chiral quark model

We study the weak vector and axial-vector form factors of first- and second-class currents for the semileptonic octet baryon decays in the spirit of the chiral quark model. Our results for the weak magnetism form factors are consistent with the conserved vector current (CVC) results. The induced pseudotensor form factors, which are highly model dependent, are small. The overall performance of the chiral quark model is quite good and in general agreement with existing experimental data. Received: 9 March 1998 / Published online: 12 August 1998     

Process Z{\rightarrow}h(A)+\gamma in the 2HDM and the experimental constraints from LEP

The one-loop branching ratios for the process are calculated in the general two Higgs doublet model (Model II), taking into account existing constraints on the model parameters. For Higgs boson masses below 50 GeV and of the fraction of such Z decays are at the level of , but can be significantly stronger for very low or high , where the dependence of these results on other model parameters like and the mass of the charged Higgs boson is found to be of little importance. The results are compared to the LEP measurements, which are sensitive to branching ratios of of the order for masses GeV, but approach for low masses. By relating the expectation to the experimental limits, constraints on the parameter space of the 2HDM are derived. Received: 28 November 1998 / Published online: 27 April 1999     

Measurements of inclusive semileptonic branching fractions of b hadrons in \boldmath Z^0z decays

A measurement of inclusive semileptonic branching fractions of b hadrons produced in Z decays is presented. An enriched Z sample is obtained with a lifetime flavour-tagging technique. The leptonic events are then selected from this sample, and classified according to their origin, which is determined by comparing the distribution of several kinematic variables using artificial neural network techniques. Using 3.6 million multihadronic events collected with the OPAL detector at energies near the Z resonance, the values are measured, where b denotes all weakly decaying b hadrons and represents either e or . The second error includes all experimental systematic uncertainties whereas the last error is due to uncertainties in modelling of the lepton momentum spectrum in semileptonic decays and b quark fragmentation. The average fraction of the beam energy carried by the weakly decaying b hadron, , is measured to be where the modelling error is dominated by the choice of b fragmentation model. The agreement between data and various semileptonic decay models and fragmentation functions is also investigated. Received: 11 June 1999 / Published online: 3 February 2000     

Semileptonic decays B_c■(η_c,J/ψ)l■_l in the “PQCD+Lattice” approach

We study the semileptonic decaysBc-→(ηc,J/ψ)l-■lusing the PQCD factorization approach with the newly defined distribution amplitudes of the B c meson and a new kind of parametrization for extrapolating the form factors which takes into account the recent lattice QCD results.We find the following main results:(a)the PQCD predictions of the branching ratios of theBc→(ηc,J/ψ)l■decays are smaller by about 5%-16%when the lattice results are taken into account in the extrapolation of the relevant form factors;(b)the PQCD predictions of the ratio Rηc,RJ/ψand of the longitudinal polarization PτareRηc=0.34±0.01,RJ/ψ=0.28±0.01,Pτ(ηc)=0.37±0.01and Pτ(J/ψ)=-0.55±0.01;and(c)after including the lattice results,the theoretical predictions slightly change:Rηc=0.31±0.01,RJ/ψ=0.27±0.01,Pτ(ηc)=0.36±0.01andPτ(J/ψ)=-0.53±0.01.The theoretical predictions of RJ/ψagree with the measurements within the errors.The other predictions could be tested by the LHCb experiment in the near future.     

On some rare weak decays of vector mesons

Some semileptonic weak decays of vector mesons are considered within the most popular quark models. Unfortunately, the predicted branching ratios are too small to make a study of these decays realistic at meson factories under construction.     

Semileptonic Decays of B_s~(**) Mesons into D_(s1) and D_(s2)~* in HQET

In the framework of the heavy quark effective theory,the leading order Isgur-Wise functions relevant to semileptonic decays of the orbitally P-wave excited B s meson states B**s,including the newly found narrow B s1(5830) and B**s2(5840) states,into the(D s1(2536),D*s2(2573)) doublet are calculated from QCD sum rules.With these universal form factors,the decay rates and branching ratios are also estimated.     

Rare Top Quark Decays t→cV in theTopcolor-Assisted Technicolor Model

We consider the rare top quark decays in the framework of topcolorassisted technicolor (TC2) model. We find that the contributions of top-pions and top-Higgs predicted by the TC2 model can enhance the SM branching ratios by as much as 6—9 orders of magnitude. i.e., in the most case, the orders of magnitude of branching ratios are Br(t→cg)～10^－5, Br(t→cZ)～10^－5, Br(t→cγ)～10^－7. With the reasonable values of the parameters in TC2 model, such rare top quark decays may be testable in the future experiments. So, rare top quark decays provide us a unique way to test TC2 model.