Weak electric and magnetic form factors for semileptonic baryon decays in a relativistic quark model (original) (raw)

Semileptonic decays of heavyΩbaryons in a quark model

Physical Review C, 2006

The semileptonic decays of Ωc and Ω b are treated in the framework of a constituent quark model developed in a previous paper on the semileptonic decays of heavy Λ baryons. Analytic results for the form factors for the decays to ground states and a number of excited states are evaluated. For Ω b to Ωc the form factors obtained are shown to satisfy the relations predicted at leading order in the heavy-quark effective theory at the non-recoil point. A modified fit of nonrelativistic and semirelativistic Hamiltonians generates configuration-mixed baryon wave functions from the known masses and the measured Λ + c → Λe + ν rate, with wave functions expanded in both harmonic oscillator and Sturmian bases. Decay rates of Ω b to pairs of ground and excited Ωc states related by heavy-quark symmetry calculated using these configuration-mixed wave functions are in the ratios expected from heavy-quark effective theory, to a good approximation. Our predictions for the semileptonic elastic branching fraction of ΩQ vary minimally within the models we use. We obtain an average value of (84± 2%) for the fraction of Ωc → Ξ (*) decays to ground states, and 91% for the fraction of Ωc → Ω (*) decays to the ground state Ω. The elastic fraction of Ω b → Ωc ranges from about 50% calculated with the two harmonic-oscillator models, to about 67% calculated with the two Sturmian models.

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

The European Physical Journal A, 2007

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 ansazt 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 and mass radii, 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.

A model for baryon structure and its application to magnetic moments and semileptonic decays

The spin 112 baryons are pictured as a composite system made out of a "core" of three valence quarks (as in the simple quark model) surrounded by a "sea" (of gluon and qQ pairs) which is specified by its total quantum numbers. We assume the sea is a SU(3) flavor octet with spin 0 or 1 but no color. This model. considered earlier. is used to obtain simultaneous fits for magnetic moments and GA/GV for semileptonic decays. These fits give predictions for nucleon spin distributions in reasonable agreement with experiment.

Phenomenological quark model for baryon magnetic moments and beta decay ratios (GA/GV)

Phys. Rev. D66: 033010, 2002, 2001

Baryon magnetic moments and beta decay ratios (GA/GV) are calculated in a phenomenological quark model. Non-static effects of pion exchange and orbital excitation are included. Good agreement with experiment is found for a combined fit to all measured baryon magnetic moments and beta decay ratios. The model predicts an antiquark content for the proton that is consistent with the Gottfried sum rule.

A New Quark Model Approach to Hyperon Semi-Leptonic Decays

A new analysis of hyperon semi-leptonic decay data is presented, based on simple and general arguments for an SU(3)-breaking structure of the couplings involved. The results obtained are compatible with those of earlier investigations and highlight the uncertainties inherent in extraction of the V us Cabibbo-Kobayashi-Maskawa matrix element from such data, and the need for complete analyses. For F and D, the results can be summarised by the ratio: F/D = 0.57 ± 0.01; while as far as the value of V us is concerned, the only conclusion to be drawn is that, insofar as SU(3) breaking is still not totally under control, the value obtained is compatible but not competitive with that obtained from kaon semileptonic decays.

Semileptonic decays of heavy Λ baryons in a quark model

Physical Review C, 2005

The semileptonic decays of Λc and Λ b are treated in the framework of a constituent quark model. Both nonrelativistic and semirelativistic Hamiltonians are used to obtain the baryon wave functions from a fit to the spectra, and the wave functions are expanded in both the harmonic oscillator and Sturmian bases. The latter basis leads to form factors in which the kinematic dependence on q 2 is in the form of multipoles, and the resulting form factors fall faster as a function of q 2 in the available kinematic ranges. As a result, decay rates obtained in the two models using the Sturmian basis are significantly smaller than those obtained using the harmonic oscillator basis. In the case of the Λc, decay rates calculated using the Sturmian basis are closer to the experimentally reported rates. However, we find a semileptonic branching fraction for the Λc to decay to excited Λ * states of 11% to 19%, in contradiction with what is assumed in available experimental analyses. Our prediction for the Λ b semileptonic decays is that decays to the ground state Λc provide a little less than 70% of the total semileptonic decay rate. For the decays Λ b → Λc, the analytic form factors we obtain satisfy the relations expected from heavy-quark effective theory at the non-recoil point, at leading and next-to-leading orders in the heavy-quark expansion. In addition, some features of the heavyquark limit are shown to naturally persist as the mass of the heavy quark in the daughter baryon is decreased.

Rare dileptonic decays of\ Lambda_b in a quark model

Arxiv preprint arXiv:1108.6129, 2011

Hadronic form factors for the rare weak transitions Λ b → Λ ( * ) are calculated using a nonrelativistic quark model. The form factors are extracted in two ways. An analytic extraction using single component wave functions (SCA) with the quark current being reduced to its nonrelativistic Pauli form is employed in the first method. In the second method, the form factors are extracted numerically using the full quark model wave function (MCN) with the full relativistic form of the quark current. Although there are differences between the two sets of form factors, both sets satisfy the relationships expected from the heavy quark effective theory (HQET). Differential decay rates, branching ratios and forward-backward asymmetries (FBAs) are calculated for the dileptonic decays Λ b → Λ ( * ) ℓ + ℓ − , for transitions to both ground state and excited daughter baryons. Inclusion of the long distance contributions from charmonium resonances significantly enhances the decay rates. In the MCN model the Λ(1600) mode is the dominant mode in the µ channel when charmonium resonances are considered; the Λ(1520) mode is also found to have a comparable branching ratio to that of the ground state in the µ channel. → N ( * ) were calculated using single component wave functions obtained from a variational diagonalization of a quark model Hamiltonian. In that calculation, quark operators were reduced to their nonrelativistic Pauli form. The decay rates obtained using the form factors extracted in that calculation were in reasonable agreement with experimental results for the semileptonic decays Λ b → Λ c ℓν ℓ and Λ c → Λℓν ℓ .

Electromagnetic and weak decays of baryons in the unquenched quark model

Journal of Physics: Conference Series, 2018

In this contribution, we discuss the electromagnetic and weak decays of baryons in the unquenched quark model and show that the observed discrepancies between the experimental data and the predictions of the constituent quark model can be accounted for in large part by the effects of sea quarks. Finally, the obtained results are discussed in terms of flavor-symmetry breaking.

Theory of Heavy Baryon Decay 1

We discuss various topics in the theory of heavy baryon decays. Among these are recent applications of the Relativistic Three Quark Model to semileptonic, non-leptonic, one-pion and one-photon transitions among heavy baryons, new higher order perturbative results on the correlator of two heavy baryon currents and on the semi-inclusive decay Λ b → X c + D