Semileptonic Decays of Heavy Lambda Baryons in a Quark Model
Semileptonic Decays of Heavy Lambda Baryons in a Quark Model

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Published: 2005

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The semileptonic decays of [Lambda]{sub c} and [Lambda]{sub 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 q2 is in the form of multipoles, and the resulting form factors fall faster as a function of q2 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 [Lambda]{sub c}, decay rates calculated using the Sturmian basis are closer to the experimentally reported rates. However, we find a semileptonic branching fraction for the [Lambda]{sub c} to decay to excited [Lambda]* states of 11% to 19%, in contradiction with what is assumed in available experimental analyses. Our prediction for the [Lambda]{sub b} semileptonic decays is that decays to the ground state [Lambda]{sub c} provide a little less than 70% of the total semileptonic decay rate. For the decays [Lambda]{sub b} → [Lambda]{sub c}, 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 heavy-quark limit are shown to naturally persist as the mass of the heavy quark in the daughter baryon is decreased.

Semileptonic Decays of Heavy Omega Baryons in a Quark Model
Semileptonic Decays of Heavy Omega Baryons in a Quark Model

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Published: 2006

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The semileptonic decays of?{sub c} and?{sub b} are treated in the framework of a constituent quark model developed in a previous paper on the semileptonic decays of heavy? baryons. Analytic results for the form factors for the decays to ground states and a number of excited states are evaluated. For?{sub b} to?{sub c} 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?{sub c} →?e+? rate, with wave functions expanded in both harmonic oscillator and Sturmian bases. Decay rates of?{sub b} to pairs of ground and excited?{sub c} 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?{sub Q} vary minimally within the models we use. We obtain an average value of (84 ± 2%) for the fraction of?{sub c} →?{sup (*)} decays to ground states, and 91% for the fraction of?{sub c} →?{sup (*)} decays to the ground state?. The elastic fraction of?{sub b} →?{sub c} ranges from about 50% calculated with the two harmonic-oscillator models, to about 67% calculated with the two Sturmian models.

Excited Charm Baryons in Semileptonic Lambda(sub)b Decay and Their Contribution to a Bjorken Sum Rule
Excited Charm Baryons in Semileptonic Lambda(sub)b Decay and Their Contribution to a Bjorken Sum Rule

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Published: 1991

Total Pages: 215

ISBN-13:

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It has recently been shown that hadrons containing a single heavy quark exhibit a new flavor-spin symmetry of QCD. We exploit this symmetry to obtain model independent predictions for the form factors for the semileptonic decay of the Lambda(sub)b to the low-lying negative parity charm baryons. We discuss the connection between these results and the slope of the universal function Zeta that determines the Lambda(sub)b->Lambda(sub)c weak form factors.

Rare Exclusive Dileptonic and Radiative Decays of [Lambda][subscript B] Baryons in a Quark Model
Rare Exclusive Dileptonic and Radiative Decays of [Lambda][subscript B] Baryons in a Quark Model

Author: Lonnie James Mott

Publisher:

Published: 2011

Total Pages: 95

ISBN-13:

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ABSTRACT: Hadronic form factors for the rare weak transitions [Lambda][subscript b] [rightarrow] [Lambda][superscript (*)] 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. Both sets of form factors are found to satisfy the relationships expecetd from the heavy quark effective theory (HQET). Differential decay rates, branching ratios and forward-backward asymmetries (FBAs) are calculated for the dileptonic decays [Lambda][subscript b][rightarrow] [Lambda][superscript (*)][ell]+[ell]-, for transitions to both ground state and excited daughter baryons. Inclusion of the long distance contributions from charmonium resonances significantly enhances the decay rates. It is found that in the MCN model the [Lambda](1600) mode is the dominant mode in the [mu] channel when charmonium resonances are considered; the [Lambda](1520) mode is also found to have a comparable branching ratio to that of the ground state in the [mu] channel. It has been found that the FBAs for decays to [Lambda](1115), [Lambda](1600) and [Lambda](1405) are less sensitive to the form of the form factors in certain kinematic regions.

INTRODUCTION TO PARTICLE PHYSICS
INTRODUCTION TO PARTICLE PHYSICS

Author: M. P. KHANNA

Publisher: PHI Learning Pvt. Ltd.

Published: 1999-01-01

Total Pages: 314

ISBN-13: 9788120312685

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This comprehensive and well-organized book focusses on the phenomeno-logical aspects of Particle Physics. It strikes a fine balance between those texts that require sophisticated mathematical physics and those that are too elementary. For, unlike in many books on the subject, which give prominence to gauge theories, the attempt here is to lay stress on phenomenology _ an aspect that needs exposure among students of high energy physics.

Heavy Quark Effective Theory
Heavy Quark Effective Theory

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Publisher:

Published: 1994

Total Pages:

ISBN-13:

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After a brief introduction, the results of application of the heavy quark effective theory to semileptonic decays of beta mesons are discussed. A nearly-model-independent extraction of {vert_bar}V{sub cb}{vert_bar} from data is described. Application of the effective theory to inclusive semileptonic decays of heavy mesons, in semileptonic decays of heavy baryons, and to the nonleptonic decays of hadrons are outlined. The authors conclude by mentioning other areas of research in this very active field.