Quark models<Superscript>⋆</Superscript>

The scope of a relativistically covariant constituent quark model of baryons based on the Bethe-Salpeter equation in instantaneous approximation is illustrated by a discussion of various baryon resonance observables such as static electromagnetic moments --including a novel calculational procedure-- form factors and helicity amplitudes, semileptonic decays as well as the systematics of two-body strong decay widths.     

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.     

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.     

Static properties and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model

We evaluate static properties and semileptonic decays for the ground state of doubly heavy Ξ, Ξ', Ξ ^* and Ω, Ω', Ω ^* baryons. Working in the framework of a nonrelativistic quark model, we solve the three-body problem by means of a variational ansatz made possible by heavy-quark spin symmetry constraints. To check the dependence of our results on the inter-quark interaction we use five different quark-quark potentials that include a confining term plus Coulomb and hyperfine terms coming from one-gluon exchange. Our results for static properties (masses, charge radii and magnetic moments) are, with a few exceptions for the magnetic moments, in good agreement with a previous Faddeev calculation. Our much simpler wave functions are used to evaluate semileptonic decays of doubly heavy Ξ, Ξ'(J = 1/2) and Ω, Ω'(J = 1/2) baryons. Our results for the decay widths are in good agreement with calculations done within a relativistic quark model in the quark-diquark approximation. An erratum to this article is available at .     

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     

Doubly heavy-quark baryon spectroscopy and semileptonic decay

Working in the framework of a nonrelativistic quark model we evaluate the spectra and semileptonic decay widths for the ground state of doubly heavy Ξ and Ω baryons. We solve the three-body problem using a variational ansatz made possible by the constraints imposed by heavy-quark spin symmetry. In order to check the dependence of our results on the inter-quark interaction, we have used five different quark-quark potentials which include Coulomb and hyperfine terms coming from one-gluon exchange, plus a confining term. Our results for the spectra are in good agreement with a previous calculation done using a Faddeev approach. For the semileptonic decay our results for the total decay widths are in good agreement with the ones obtained within a relativistic quark model in the quark-diquark approximation.     

SU(3) symmetry breaking for masses, magnetic moments and sizes of baryons

We use the SU(3) Skyrme model to investigate the effects of symmetry breaking imposed by different pseudoscalar meson masses on the structure of baryons. Specifically, we calculate their mass splittings, magnetic moments, charge radii, semileptonic decays as well as different strangeness contents of the proton. Since the Skyrme soliton is allowed to deform under the pressure of the symmetry breaking we find significant variations in baryon sizes with respect to strangeness.     

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.     

Baryon properties in the relativistic quark model

Properties of heavy and strange baryons are investigated in the framework of the relativistic quark-diquark picture. It is based on the relativistic quark model of hadrons, which was previously successfully applied for the calculation of meson properties. It is assumed that two quarks in a baryon form a diquark and baryon is considered as the bound quark-diquark system. The relativistic effects and diquark internal structure are consistently taken into account. Calculations are performed up to rather high orbital and radial excitations of heavy and strange baryons. On this basis the Regge trajectories are constructed. The rates of semileptonic decays of heavy baryons are calculated. The obtained results agree well with available experimental data.     

Charmed baryons circa 2015

This is essentially an update of Ref. [1] [H. Y. Cheng, Int. J. Mod. Phys. A 24 (Suppl. 1), 593 (2009)], a review of charmed baryon physics around 2007. Topics covered in this review include the spectroscopy, strong decays, lifetimes, nonleptonic and semileptonic weak decays, and electromagnetic decays of charmed baryons.     

Heavy quark symmetry at large recoil: the case of baryons

We analyze the large recoil behaviour of heavy baryon transition form factors in semileptonic decays. We use a generalized Brodsky-Lepage hard scattering formalism where diquarks are considered as quasi-elementary constituents of baryons. In the limit of infinitely heavy quark masses the large recoil form factors exhibit a new model-independent heavy quark symmetry which is reminiscent but not identical to the Isgur-Wise symmetry at low recoil.     

Role of hyperfine mixing in b→c semileptonic decays of doubly-heavy baryons

We analyze the effects of hyperfine mixing in b → c semileptonic decays of doubly heavy baryons.We qualitatively confirm the results by W.Roberts and M.Pervin in Int.J.Mod.Phys.A,2009,24: 2401– 2413,finding that mixing has a great impact on those transitions.However,predictions without mixing differ by a factor of 2 and this discrepancy translates to the mixed case where large differences in decay widths are observed between the two calculations.     

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.     

Heavy-quark physics

Recent advances as well as some problems in physics of bottom and top quarks are discussed.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.39.-x Phenomenological quark models - 13.20.-v Leptonic, semileptonic, and radiative decays of mesons - 13.30.-a Decays of baryons - 13.60.Rj Baryon production     

Quark-diquark approximation of the three-quark structure of baryons in the quark confinement model

Octet (1/2⁺) and decuplet (3/2⁺) baryons as relativistic three-quark states are investigated using the quark confinement model (QCM), the relativistic quark model, based on some assumptions about hadronization and quark confinement. The quark-diquark approximation of the three-quark, structure of baryons is proposed. In the framework of this approach, the main low-energy characteristics of baryons, such as magnetic moments, electromagnetic radii and form factors, the ratio of axial and vector constants in semileptonic baryon decays, strong form factors and decay widths, are described. The obtained results agree with experimental data.     

Heavy to light baryon weak form factors in the lightcone constituent quark model

Heavy to light baryon weak form factors are investigated in a lightcone constituent quark model. In a SU(4) symmetry broken scheme, both charged and neutral weak current-induced form factors are calculated at theq ² = 0 point including the leading relativistic effects in the spin composition of baryons. The corresponding semileptonic decays are described by assuming dipole dependence of form factors onq ².     

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.     

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.     

Predictions for semileptonic decay rates of charmed baryons in the quark confinement model

Baryons as relativistic three-quark states are investigated in the quark confinement model (QCM), a relativistic quark model based on some assumptions about hadronization and quark confinement. In the framework of the quark-diquark approximation of the three-quark structure of baryons, the main characteristics of light (noncharmed) baryons are calculated. The obtained results agree with experimental data. Predictions are also given for semileptonic decay of charmed baryons and differential production cross-sections in quasielastic neutrino scattering of charmed baryons.     

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.