Nonmesonic Weak Decay of A-Hypernuclei within Independent-Particle Shell-Model

Abstract

Abstract. After a short introduction to the nonmesonic weak decay (NMWD) ΛN → nN of Λ-hypernuclei we discuss the long-standing puzzle on the ratio Γ n /Γ p , and some recent experimental evidences that signalized towards its final solution. Two versions of the Independent-Particle-ShellModel (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are: (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 quasi-stationary and are described by Breit-Wigner distributions, whose widths are estimated from the experimental data. We evaluate the coincidence spectra in Λ He, is interpreted within the IPSM . We found that the shapes of all the spectra are basically tailored by the kinematics of the corresponding phase space, depending very weakly on the dynamics, which is gauged here by the one-meson-exchange-potential. In spite of the straightforwardness of the approach a good agreement with data is achieved. This might be an indication that the finalstate-interactions and the two-nucleon induced processes are not very important in the decay of this hypernucleus. We have also found that the π + K exchange potential with soft vertex-formfactor cutoffs (Λ π ≈ 0.7 GeV, Λ K ≈ 0.9 GeV), is able to account simultaneously for the available experimental data related to Γ p and Γ n for

Nonmesonic weak decay of charmed hypernuclei

“…where we are using the notation J J 2 1 = + ˆ. The values for J I and J C are taken from table 1 of [65], assuming that they hold also for charmed nuclei, that is J 3 2 C = and J I = 1. The experimentally measured ground-state spins in 11 C and C 12 L are, respectively, 3 2and 1 -, as 5 We adhere to the notation used in most of the recent [13,14,17] and past [31,34] literature on charmed hypernuclei, in that a charmed c L + hypernucleus with A baryons and total electric charge Z receives the name of ordinary nuclides with Z protons.…”

“…But in the absence of experimental or lattice results on the spin-dependent forces in the N c Linteraction that ultimately lead to the splitting between the two states, we have simply assumed for N 12 c L + the measured value of J I in 12 L C, although a smaller splitting can be expected on the account of the larger mass of the c L + that suppresses spin-dependent forces. The corresponding values for the factors F J j n are listed in table 2 of [65].…”

“…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].…”