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Title: {sigma} meson exchange effect on non-mesonic hypernuclear weak decay observables

Abstract

We analyze the influence of {sigma} meson exchange on the main non-mesonic hypernuclear weak decay observables: Total rate {gamma}{sub NM}, neutron-to-proton branching ratio {gamma}{sub n/p}, and proton asymmetry parameter a{sub {lambda}}. The {sigma} meson exchange is added to the standard strangeness-changing weak {lambda}N{yields}NN transition potential, which includes the exchange of the complete pseudoscalar and vector mesons octet ({pi},{eta},K,{rho},{omega},K{sup *}). Using a shell model formalism, the {sigma} meson weak coupling constants are adjusted to reproduce the recent {gamma}{sub NM} and {gamma}{sub n/p} experimental data for {sub {lambda}}{sup 5}He. Numerical results for the remaining observables of {sub {lambda}}{sup 5}He and all the observables of {sub {lambda}}{sup 12}C decays are presented. They clearly show that the addition of the {sigma} meson improves the agreement with the data. However, its effect it is not enough to reproduce well the a{sub {lambda}} values, which means that other improvements of the model must be explored to explain the puzzle posed by the experiments.

Authors:
;  [1]
  1. Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 67, 1900 La Plata (Argentina)
Publication Date:
OSTI Identifier:
20771260
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 73; Journal Issue: 2; Other Information: DOI: 10.1103/PhysRevC.73.024309; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ASYMMETRY; BOSON-EXCHANGE MODELS; BRANCHING RATIO; CARBON 12; COUPLING CONSTANTS; HELIUM 5; HYPERNUCLEI; LAMBDA BARYONS; NEUTRONS; NUCLEAR DECAY; NUCLEON-HYPERON INTERACTIONS; POTENTIALS; PROTONS; PSEUDOSCALAR MESONS; SHELL MODELS; STRANGENESS; VECTOR MESONS; WEAK INTERACTIONS

Citation Formats

Barbero, C., and Mariano, A. {sigma} meson exchange effect on non-mesonic hypernuclear weak decay observables. United States: N. p., 2006. Web. doi:10.1103/PhysRevC.73.024309.
Barbero, C., & Mariano, A. {sigma} meson exchange effect on non-mesonic hypernuclear weak decay observables. United States. doi:10.1103/PhysRevC.73.024309.
Barbero, C., and Mariano, A. Wed . "{sigma} meson exchange effect on non-mesonic hypernuclear weak decay observables". United States. doi:10.1103/PhysRevC.73.024309.
@article{osti_20771260,
title = {{sigma} meson exchange effect on non-mesonic hypernuclear weak decay observables},
author = {Barbero, C. and Mariano, A.},
abstractNote = {We analyze the influence of {sigma} meson exchange on the main non-mesonic hypernuclear weak decay observables: Total rate {gamma}{sub NM}, neutron-to-proton branching ratio {gamma}{sub n/p}, and proton asymmetry parameter a{sub {lambda}}. The {sigma} meson exchange is added to the standard strangeness-changing weak {lambda}N{yields}NN transition potential, which includes the exchange of the complete pseudoscalar and vector mesons octet ({pi},{eta},K,{rho},{omega},K{sup *}). Using a shell model formalism, the {sigma} meson weak coupling constants are adjusted to reproduce the recent {gamma}{sub NM} and {gamma}{sub n/p} experimental data for {sub {lambda}}{sup 5}He. Numerical results for the remaining observables of {sub {lambda}}{sup 5}He and all the observables of {sub {lambda}}{sup 12}C decays are presented. They clearly show that the addition of the {sigma} meson improves the agreement with the data. However, its effect it is not enough to reproduce well the a{sub {lambda}} values, which means that other improvements of the model must be explored to explain the puzzle posed by the experiments.},
doi = {10.1103/PhysRevC.73.024309},
journal = {Physical Review. C, Nuclear Physics},
number = 2,
volume = 73,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2006},
month = {Wed Feb 15 00:00:00 EST 2006}
}
  • The nonmesonic weak decay of {Lambda} hypernuclei is studied in a relativistic shell model framework which includes a full strangeness-changing weak {Lambda}{ital N}{r_arrow}{ital NN} One-Boson-Exchange transition potential as well as a realistic {Lambda}{ital N} short-range correlation function. The total decay rate and the proton asymmetry, which represents a measure of the parity-violating to parity-conserving amplitudes, are in agreement with present experimental errors while the neutron-to-proton-induced ratio differs by more than a factor of two. In general, the observables were found to be dominated by the pion-exchange mechanism since the contributions of heavier mesons are suppressed by form factors and short-rangemore » correlations. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less
  • The weak decays of strange mesons and free hyperons strongly favor {Delta}I=1/2 amplitudes over {Delta}I=3/2 amplitudes. It is now known to what extent this rule applies to the non-mesonic interactions of the type {Lambda}p {yields} np and {Lambda}n {yields} nn. This paper examines existing data on non-mesonic decays of light hypernuclei in order to obtain a quantitative estimate of the relative strength of the two isospin channels., The data show that a pure {Delta}I=1/2 decay amplitude is ruled out at the 1.6{sigma} level, and favor a solution where either: (1) both isospin channels contribute about equally, or (2) the {Delta}I=3/2more » channel dominates by an order of magnitude.« less
  • The weak decays of strange mesons and free hyperons strongly favor {Delta}I=1/2 amplitudes over {Delta}I=3/2 amplitudes. It is now known to what extent this rule applies to the non-mesonic interactions of the type {Lambda}p {yields} np and {Lambda}n {yields} nn. This paper examines existing data on non-mesonic decays of light hypernuclei in order to obtain a quantitative estimate of the relative strength of the two isospin channels., The data show that a pure {Delta}I=1/2 decay amplitude is ruled out at the 1.6{sigma} level, and favor a solution where either: (1) both isospin channels contribute about equally, or (2) the {Delta}I=3/2more » channel dominates by an order of magnitude.« less
  • In the meson-theoretical potential model for the study of the nonmesonic decay rates and asymmetries of hypernuclei, for the first time, the axial-vector a{sub 1} meson (J{sup PC}=1{sup ++},m{sub a{sub 1}}=1230 MeV) is introduced. The a{sub 1} meson is the chiral partner of the {rho} meson and has been treated in the meson-pair exchange framework as {rho}{pi}/a{sub 1} and {sigma}{pi}/a{sub 1}. This is analogous to the treatment of {rho} and {sigma} exchange in our model. The a{sub 1}-meson exchange is found to give remarkable modifications of the parity-conserving decay potentials ({sup 1,3}S{yields}{sup 1,3}S and {sup 3}S{sub 1}{yields}{sup 3}D{sub 1}) atmore » short range r{<=}1 fm. As a result, the calculated intrinsic asymmetry parameter {alpha}{sub {lambda}} for {sub {lambda}}{sup 5}He becomes very small and positive in good agreement with the recent high-quality experimental data. The calculated small values of {alpha}{sub {lambda}} are well compared with the data for {sub {lambda}}{sup 11}B and {sub {lambda}}{sup 12}C within error bars. The inclusion of the a{sub 1} meson also improves the {gamma}{sub n}/{gamma}{sub p} ratios and leads to a consistent explanation for the existing nonmesonic weak decay data of the light {lambda} hypernuclei (A{<=}12). The results calculated in the {pi}+2{pi}/{rho}+2{pi}/{sigma}+{omega}+K+{rho}{pi}/a{sub 1}+{sigma}{pi}/a{sub 1} exchange interaction model are presented together with the estimates without a{sub 1}. Also, the derivation of the expression for the proton asymmetry is described in some detail to elucidate the calculation procedures and phase conventions.« less