Radiative decays of heavy baryons with heavy quark symmetry

The decay widths for the radiative decays of heavy baryons are calculated in the heavy quark effective theory. Introducing the interpolating fields for heavy baryons we obtain the transition matrix elements and the corresponding decay widths. Considering theSU(6) flavor-spin wave functions for heavy baryons, the coupling constants are calculated in the nonrelativistic quark model. Since the masses of the heavy baryons are not available, we have taken the predicted bag model masses. We find our results are quite different from that of the heavy quark bag model calculations.     

Spin,helicity and flavour patterns in exclusive decays of bottom mesons into baryon-antibaryon pairs

I use the constituent quark model to calculate the exclusive decays of bottom mesons into ground state baryon-antibaryon pairs mediated by the weakb→c and b→u transitions. TheW-exchange contributions to these decays are found to be negligible. For theW-decay contributions I find that the simple colour-flavour structure of the 1/2⁺ and 3/2⁺ ground state baryons together with the current-current nonleptonic Hamiltonian leads to many simple and testable predictions. Notable among these is the predicted vanishing of decays involving 3/2⁺ baryons as in \(\overline {B^0 } (B^ - ) \to 3/2^ + \overline {1/2^ + } \) and \(\overline {B^0 } (B^ - ) \to 3/2^ + \overline {3/2^ + } \) . An experimental verification of these selection rules would test the chirality of the basicb→c andb→u transitions. I also derive predictions for the polarization of the final state baryons depending on the assumed mechanism of quark pair creation. These predictions can be checked in the cases where the final state baryons are weakly decaying spin 1/2 hyperons and charmed baryons.     

Semi-leptonic decays in the model of Bars,Halpern, and Yoshimura

Semi-leptonic decays are investigated in the gauge theory of Bars, Halpern and Yo Yoshimura, using elementary baryons rather than quarks. It is proved that in order to get a correct d/f ratio in these decays it is necessary to use an (8,8) spin-zero hadron field, together with another multiplet of spin-zero hadrons. The tree approximation is shown not to be sufficient to calculate the decay amplitudes correctly.     

B重子半轻子衰变的对称性

在无粲B重子非轻子衰变研讨基础上,进一步探讨了B重子三体和四体半轻子衰变的SU(3)f对称性,得到一系列可能衰变道衰变几率的对称关系.期待即将进行的高能实验来检验这些关系,从而验证标准模型的适用性或是否存在超标准模型的新物理信息.     

Weak annihilation in charm baryon decays — A re-evaluation

We discuss weak decays of charm baryons taking the mode Λ _c ⁺ →Δ⁺⁺ K ^? as the starting point of our analysis. This channel which can occur only due to weak annihilation has been seen at the ISR. Hence we conclude that weak annihilation is very significant for baryons. Further tests of this picture are listed, in particular concerning charm-strange baryons. We argue that τ(D°)~τ(Λ _c ⁺ )<τ(D ⁺) suggests that baryon and meson decays should be treated on an equal footing even when weak annihilation is included. We describe a framework based on evolution equations where this can be done.     

Semileptonic bc to cc and bb to bc baryon decays and heavy quark spin symmetry

We study the semileptonic decays of the lowest-lying bc baryons to the lowest-lying cc baryons (Ξ (*) bc →Ξ (*) cc and Ω ( *) bc →Ω (*) cc ),in the limit m b,m c Λ QCD and close to the zero recoil point.The separate heavy quark spin symmetries make it possible to describe all these decays using a single form factor.We also show how these constraints can be used to test the validity of different quark model calculations.bb to bc baryon decays are also discussed.     

Joint angular decay distributions in exclusive weak decays of heavy mesons and baryons

We present the results of a comprehensive analysis of the angular decay distributions occurring in the weak exclusive decays of the lowest lying charm and bottom mesons and baryons. We deal with both semileptonic and nonleptonic decays and discuss various decay channels and their subsequent cascade decay chains including lepton mass effects. In the case of baryons we include polarization effects for the parent charm or bottom baryon. We list in table form general formulae which allow one to write down the joint angular decay distributions for the cascade decaysA→B(→b ₁+...+b _n )+C(→c ₁+...+c _n ), for all spin casess _A ≤1/2 ands _B ,s _C ≤3/2 for the prominent decays ofB andC. Two examples involving meson and baryon decays are discussed in detail.     

Dipion decays of heavy baryons

Compared with the charmed baryons, the bottom baryons are not very well known, either experimentally or theoretically. In this paper, we investigate the dipion strong decays of the P-wave and D-wave excited bottom baryons in the framework of the QPC model. We also extend the same analysis to the charmed baryons.     

Heavy Quark Spin Symmetry and Heavy Baryons: Electroweak Decays

Heavy quark spin symmetry is discussed in the context of single and doubly heavy baryons. A special attention is paid to the constraints/simplifications that this symmetry imposes on the non-relativistic constituent quark model wave functions and on the b ?? c semileptonic decays of these hadrons.     

Radiative corrections to semileptonic decays of charged hyperons

We have studied the radiative corrections to the lepton energy spectrum in semileptonic hyperon decays. The calculation is performed relativistically for the baryons as well as for the leptons, under the assumption of the effective current-current interaction of the V-?A type for the baryonic part. We obtain the explicit formula of radiative corrections to the lepton energy spectrum which we can exactly evaluate in case of charged hyperon decays. Numerical values of the radiative corrections to the decays rate and the shape of the lepton energy spectrum are also given for some decay modes. It is shown that the spectral shape is little affected by the radiative corrections.     

Pseudoscalar or vector meson production in non-leptonic decays of heavy hadrons

We have addressed the study of non-leptonic weak decays of heavy hadrons (\(\Lambda _b, \Lambda _c, B\) and D), with external and internal emission to give two final hadrons, taking into account the spin-angular momentum structure of the mesons and baryons produced. A detailed angular momentum formulation is developed which leads to easy final formulas. By means of them we have made predictions for a large amount of reactions, up to a global factor, common to many of them, that we take from some particular data. Comparing the theoretical predictions with the experimental data, the agreement found is quite good in general and the discrepancies should give valuable information on intrinsic form factors, independent of the spin structure studied here. The formulas obtained are also useful in order to evaluate meson-meson or meson-baryon loops, for instance of B decays, in which one has PP, PV, VP or VV intermediate states, with P for pseudoscalar mesons and V for vector meson and lay the grounds for studies of decays into three final particles.     

1/<Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> countings in baryons

The 1/N _c -power countings for baryon decays and configuration mixings are determined by means of a nonrelativistic quark picture. Such countings are expected to be robust under changes in the quark masses and, therefore, valid as these become light. It is shown that excited baryons have natural widths of \(\mathcal{O}(N_c^0 )\). These dominant widths are due to the decays that proceed directly to the ground-state baryons, with cascade decays being suppressed to \(\mathcal{O}(1/N_c )\). Configuration mixings, defined as mixings between states belonging to different O(3) × SU(2N _f ) multiplets, are shown to be subleading in an expansion in \(1/\sqrt {N_c }\) when they involve the ground-state baryons, while the mixings between excited states can be \(\mathcal{O}(N_c^0 )\).     

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.     

Weak decays of charmed baryons

We use the quark model framework to calculate the weak decays of the lowest lying charmed baryons into ground state baryons and mesons. We present detailed results on the predicted flavour and multipole composition of the final state configurations which can be tested in the near future. For the decays 1/2⁺→1/2⁺+0^? we also give symmetry and current algebra estimates which we compare with the quark model results. Semileptonic branching ratios in charmed baryon decays are calculated to be of the order of ～5%. The total lifetime of charmed baryons is predicted to be ～7 10^?14 s which is 5–10 times smaller than the free quark model estimate.     

Strange baryon production in hadronic Z0 decays

The production of the $J^{P}={1?er 2}^{+}$ octet baryons Λ and Ξ^?, the $J^{P}={3?er 2}^{+}$ decuplet baryons Σ(1385)^±Ξ(1530)⁰, and Ω^?, and the $J^{P}={3?er 2}^{-}$ orbitally excited state Λ(1520) has been measured in a sample of approximately 3.65 million hadronic Z⁰ decays. The integrated rates and the differential cross-sections as a function of x _E, the scaled energy, are determined. The differential cross-sections of the Λ and Ξ^? baryons are found to be softer than those predicted by both the JETSET and HERWIG Monte Carlo generators. The measured baryon yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is allowed. The yields are further compared with a thermodynamic model of hadron production which includes the production of orbitally excited mesons and baryons. The momentum spectra of Λ, Ξ^?, Σ(1385)^±Ξ(1530)⁰, and Λ(1520) are also compared to the predictions of an analytical QCD formula.     

B meson decays to baryons in the diquark model

We study B meson decays to two charmless baryons in the diquark model, including strong and electroweak penguins as well as the tree operators. It is shown that penguin operators can enhance considerably, but affect only slightly, where and are non-strange and strange baryons, respectively. The dependence of the decay rates due to tree–penguin interference is illustrated. In principle, some of the modes could dominate over for , but in general the effect is milder than their mesonic counterparts. This is because the operator can only produce vector but not scalar diquarks, while the opposite is true for and . Predictions from the diquark model are compared to those from the sum rule calculation. The decays and inclusive baryonic decays are also discussed. Received: 27 December 2001 / Published online: 5 April 2002     

Weak decays of doubly heavy baryons: “decay constants”

Inspired by the recent observation of the Ξ_c~+_c~+)by the LHCb Collaboration, we explore the "decay constants" of doubly heavy baryons in the framework of QCD sum rules. With the Ξ_cc),Ξ_(bc),Ξ_(bb), and ?_(cc),?_(bc),?_(bb) baryons interpolated by three-quark operators, we calculate the correlation functions using the operator product expansion and include the contributions from operators up to dimension six. On the hadron side, we consider both contributions from the lowest-lying states with JP=1/2~+ and from negative parity baryons with JP=1/2~-. We find that the results are stable and the contaminations from negative parity baryons are not severe. These results are ingredients for the QCD study of weak decays and other properties of doubly-heavy baryons.     

Spectroscopy of charmed baryons

We have fitted the masses and elastic widths of the S=0 baryons in the context of the QCD-improved quark shell model. All states in theN=0, 1, 2 and 3 harmonic oscillator bands have been included. Three models for the decay of these states have been studied, and it is concluded that the usual spectator model for the decays must be modified. Many resonances in theN=2 and 3 bands were found to decouple from the πN channel, supporting a previous solution to the missing resonance puzzle. No evidence has been found for the tensor force, while conflicting data exist for the 3-body spin orbit term. We also have found evidence that the contact force varies with band. The (56,1^?) multiplet is lower than expected.     

Leptonic decays of baryons

Formulae are obtained for the differential decay rate, lepton spectrum, and partial lifetime for the leptonic decays of baryons, which cover effects down to the order of one percent. A weak, linearq ²-dependence of the form factors is included, which should be a sufficiently good approximation in the physicalq ²-range allowed in the decays. The one percent discrepancy arises as a consequence of the above-mentioned approximation to the form factors, whose value and slope atq ²=0 are left open in the formulae;SU(3) symmetry, CVC, and PCAC yield an estimate for these parameters.