Kinetic energy sum spectra in nonmesonic weak decay of hypernuclei
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2008-10-16
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Barbero, Cesar
Galeão, Alfredo P. [UNESP]
Hussein, Mahir S.
Krmpotić, Francisco
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We evaluate the coincidence spectra in the nonmesonic weak decay (NMWD) ΛN→nN of Λ hypernuclei Λ4He, Λ5He, Λ12C, Λ16O, and Λ28Si, as a function of the sum of kinetic energies EnN=En+EN for N=n,p. The strangeness-changing transition potential is described by the one-meson-exchange model, with commonly used parametrization. Two versions of the independent-particle shell model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are as follows: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into account and (b) IPSM-b, where the highly excited hole states are considered to be quasistationary and are described by Breit-Wigner distributions, whose widths are estimated from the experimental data. All np and nn spectra exhibit a series of peaks in the energy interval 110 MeV <EnN<170 MeV, one for each occupied shell-model state. Within the IPSM-a, and because of the recoil effect, each peak covers an energy interval proportional to A-1, going from ≅4 MeV for Λ28Si to ≅40 MeV for Λ4He. Such a description could be pretty fair for the light Λ4He and Λ5He hypernuclei. For the remaining, heavier, hypernuclei it is very important, however, to consider as well the spreading in strength of the deep-hole states and bring into play the IPSM-b approach. Notwithstanding the nuclear model that is employed the results depend only very weakly on the details of the dynamics involved in the decay process proper. We propose that the IPSM is the appropriate lowest-order approximation for the theoretical calculations of the of kinetic energy sum spectra in the NMWD. It is in comparison to this picture that one should appraise the effects of the final-state interactions and of the two-nucleon-induced decay mode. © 2008 The American Physical Society.
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Physical Review C - Nuclear Physics, v. 78, n. 4, 2008.