Kinetic energy sum spectra in nonmesonic weak decay of hypernuclei

Abstract

We evaluate the coincidence spectra in the nonmesonic weak decay (NMWD) N → nN of hypernuclei 4 He, 5 He, 12 C, 16 O, and 28 Si, as a function of the sum of kinetic energies E nN = E n + E N 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 < E nN < 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 28 Si to ∼ =40 MeV for 4 He. Such a description could be pretty fair for the light 4 He and 5 He 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.

Many-body cascade calculation of final state interactions in _\Lambda ^{12}C nonmesonic weak decay

“…where ε's are single-particle energies, and = M − M. (The non-stationary version of the IPSM is discussed in [37]. )…”

“…The main aim of this work is to analyze to which extent the FSI, accounted for by means of the CRISP code, modify the spectra obtained within the independent particle shell model (IPSM) [35][36][37][38][39][40], and to find out to what extent it is possible to explain the experimental data. The IPSM spectra are used to start up the cascade process.…”

Nonmesonic weak decay of charmed hypernuclei

“…with J M given by equation (36) (for the K p + OME model). From previous works of [54,55,58,65,75,76], we know that to describe the NMWD in Λ hypernuclei with open-shell cores within the IPSM it is enough to make the replacement…”

Relativistic model for the nonmesonic weak decay of single-lambda hypernuclei

“…In what follows we will make use of analogies with NR calculations. From previous works [19][20][21][22][23][24] done by our group, we know that to describe the hypernuclei with open-shell cores within the IPSM it is enough to do the following replacement in equation (50)…”

“…) mesons [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] . The coupling constants at the strong vertices can be taken from different OME models for the NN interaction, while those at the weak vertices can be extracted from free Λ decay data and making use of soft meson theorems and SU 6 W ( ) symmetry [7].…”