Semileptonic Decays of Heavy Mesons to Light Pseudoscalar Mesons in the BS Formalism

The decay processes from heavy to light pseudoscalar mesons such as π, K, η,η' are studied in a relativistic constituent quark model based on the BS formalism. It is emphasized that the negative energy projector operators's contributions in the BS wavefunctions for light pseudoscalar mesons have to be considered. By taking into account these contributions, the previously encountered difficulties in calculating the decay constants and form factors are found to be removed. A11 the form factors for transitions such as D→π, D→K, D_s→K, D_s→η, D_s→η', B→π, B_s→K are estimated and the branching ratios for these semileptonic decays are calculated. The results of our calculations are consistent with experimental values.     

Inclusive decays and lifetimes of doubly-charmed baryons

The analysis of singly-charmed hadrons has been extended to the case of doubly-charmed baryons, , and . Doubly-charmed baryons are described as a system containing a heavy cc diquark and a light quark, as in the case of a heavy–light meson. This leads to preasymptotic effects in semileptonic and nonleptonic decays that are essentially proportional to the meson wave function. Interplay between preasymptotic effects in semileptonic and/or nonleptonic decay rates leads to very clear predictions for semileptonic branching ratios and lifetimes of doubly-charmed baryons. Received: 21 January 1999 / Published online: 20 May 1999     

Study of semileptonic and nonleptonic decays of the B<Subscript>c</Subscript><Superscript>-</Superscript> meson

We evaluate semileptonic and two-meson nonleptonic decays of the B _c ^- meson in the framework of a nonrelativistic quark model. The former are done in spectator approximation using one-body current operators at the quark level. Our model reproduces the constraints of heavy-quark spin symmetry obtained in the limit of infinite heavy-quark mass. For the two-meson nonleptonic decays we work in factorization approximation. We compare our results to the ones obtained in different relativistic approaches.     

Weak decays of charm and quark masses

We calculate the effects of finite quark masses for the semileptonic and nonleptonic decays of charmed particles. The total lifetimes of charmed particles are not sensitive to the masses of the quarks in the final state. However the semileptonic branching ratios changes considerably. Using conventional constituent quark masses, one expect e.g. B_e(D⁺)≈ 21%. The brancing ratios and lifetimes of the charmed particles are estimated, taking into account the annihilation hypothesis.     

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 and Nonleptonic Decays of B s Mesons

We investigate the semileptonic and nonleptonic decays of B _s mesons. We work within the context of nonrelativistic constituent quark models. We calculate the different form factors that parameterize the hadron matrix elements.     

Enhancement of hadronic b quark decays

A class of previously unknown strong-interaction corrections is found to enhance the rate of nonleptonic decays of the quark by 5%-8%. This effect decreases the predicted fraction of semileptonic decays and brings it into fair agreement with experimental results. As well as solving a long-standing puzzle of measurements disagreeing with the standard model prediction, our work suggests a way for future precise studies of nonleptonic quark decays and their application to searching for "new physics."     

Right-handed current effect on inclusive decays of theB meson

Recent experimental values for the inclusive semileptonic decay branching ratio of theB meson are low compared to the spectator model expectation. That branching ratio is investigated in the right-handed current model. The right-handed current could enhance the nonleptonic decay mode, thereby suppressing the semileptonic branching ratio. Then, the quark mixing matrix of the right-handed sector is restricted to be of one special type and the right-handed neutrino has to be the heavy Dirac one.     

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.     

Pseudo-Scalar Meson Wavefunctions and Exclusive Decays of D and B Mesons

Pseudo-scalar meson wavefunctions are proposed. Their moments are consistent with the QCD sum rule and lattice gauge results. The radii and transverse momenta of these wavefunctions are discussed. We develop a method and apply these wavefunctions to calculate the exclusive semileptonic and nonleptonic decays of D-and B-mesons. The results are in good agreement with experiments. We find an upper limit on |V_ub| as 0.01. We also find that the parameter ξ may not be zero in nonleptonic decays of D-and B-mesons.     

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.     

Long distance contributions in D → Vγ decays

Using the factorization scheme for the nonleptonic D → > VV ₀ weak amplitudes, we classify all diagrams which arise in D → Vγ decays and calculate them with the help of the hybrid model which combines the heavy quark effective theory and the chiral Lagrangian approach. Thus we determine the long distance contribution to the amplitudes of Cabibbo allowed and Cabibbo suppressed D → Vγ decays. The calculation of the expected range of the branching ratios of nine different D → Vγ channels is compared with results of other approaches. The present work establishes an increase of the parity violating contribution in these decays in comparison with previous analyses.     

Heavy-heavy form factors and generalized factorization

We reanalyze and data to extract a set of parameters which give the relevant hadronic matrix elements in terms of factorized amplitudes. Various sources of theoretical uncertainties are studied, in particular those depending on the model adopted for the form factors. We find that the fit to the branching ratios substantially depends on the model describing the Isgur-Wise function and on the value of its slope. This dependence can be reduced by substituting the with suitable ratios of non-leptonic to differential semileptonic BRs. In this way, we obtain a model-independent determination of these parameters. Using these results, the form factors at can be extracted from a fit of the . The comparison between the form factors obtained in this way and the corresponding measurements in semileptonic decays can be used as a test of (generalized) factorization free from the uncertainties due to heavy-heavy form factor modeling. Finally, we present predictions for as-yet-unmeasured and branching ratios and extract and from decays. We find MeV and MeV, in good agreement with recent measurements and lattice calculations. Received: 7 October 1998 / Revised version: 4 December 1998 / Published online: 20 May 1999     

The New Clue to Understanding fo(975) Meson From Ds Decays

Based on the understanding of nonleptonic decays of charmed meson, the relative ratio Br(D_s⁺→f₀(975)π⁺/Br(D_s⁺→фπ⁺) is calculated. We argue that only (ss) component of f₀(975) contributes to it dominantly. The numerical result proves f₀(975) to be almost a pure (ss) state if the newly measured resultant value of the decay is trustable, and the conclusion is very usefulinformation as a clue for clarifying up the puzzle of 0⁺⁺ meson f₀(975).     

Two body nonleptonic decays of Λb involving proton

We study some nonleptonic decays of Λ_b-baryon involving transition of a heavy to light quark, using nonrelativistic quark model for form factors. The decay rates for two such decays are consistent with the data available. Also these decays can give us information on the CKM matrix element |V_Ub|.     

Heavy-to-Light Form Factors in the Quark Model with Infrared Heavy-Quark Propagators

We calculate the heavy-to-light form factors in a relativistic quark model with infrared heavy-quark propagators. Their -dependence in the physical region is defined by two parameters: the “infrared” parameter characterizing the infrared behaviour of the heavy quark and the mass difference of the heavy meson and the heavy quark . It is found that the values of the and form factors at are in excellent agreement with the available experimental data and other approaches whereas for transitions these values are found to be larger than those of several other models. The obtained form factors are used to calculate the widths of the semileptonic decays of and mesons. A comparison of our results with available experimental data and other approaches is presented. Received January 31, 1997; revised July 15, 1997; accepted for publication January 20, 1998     

Weak decays of heavy quarks

To investigate the role of real gluons in heavy meson weak decays, we compute the first-order QCD corrections to the total rate for the weak decay of a heavy quark. We find that to this order there are no leading log contributions. Furthermore, the first-order QCD corrections depress the total decay rate, although they provide an enhancement of the nonleptonic rate over the semileptonic rate. We discuss the relevance of our results to the usual picture of QCD enhancements based on short-distance expansions of weak decay amplitudes.     

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.     

The Λc and its inclusive nonleptonic decay

The inclusive nonleptonic decay of the Λ_c⁺ is reanalyzed using a nonrelativistic quark model representation of the Λ_c⁺- wavefunction. It is shown that the same approximation which leads to the familiar spectator and annihilation type contributions naturally also gives interference terms as a direct consequence of Fermi statistics. Numerical estimates which include these novel contributions, are presented for the Λ_c⁺ lifetime and semileptonic branching ratio.     

Semileptonic Decays of Bc Meson to a P—Wave Charmonium State χc or hc

The semileptonic decays of meson Bc to a P-wave charmonium state χc(3PJ) or hc(1P1)are computed.The results show that the decays are sizable so they are accessible in Tevatron and LHC,especially,with the detectors LHCB and BTeV in the foreseeable future,and of them,the one to the 1P1 charmonium state potentially offers us a novel window to see the unconfirmed hc particle.In addition,it is pointed out that since the two charmonium radiative decays χc (3P1,2)→J/ψ γ have sizable branching ratios,the cascade decays of the concerned decays and the charmonium radiative decays may affect the result of observing Bc meson through the semileptonic decays Bc→J/ψ l vl substantially.