Role of the axial vector a{sub 1}-meson exchange in hypernuclear nonmesonic weak decays
- Laboratory of Physics, Faculty of Medicine, University of Miyazaki, Kiyotake, Miyazaki 889-1692 (Japan)
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}) at 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.
- OSTI ID:
- 21189917
- Journal Information:
- Physical Review. C, Nuclear Physics, Vol. 77, Issue 4; Other Information: DOI: 10.1103/PhysRevC.77.044605; (c) 2008 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2813
- Country of Publication:
- United States
- Language:
- English
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