Estimate of the parity-violatingα-decay width of the0+,T=1st

Abstract

A full two-body shell-model calculation has been used to estimate the pion-exchange contribution to the parity-violating u decay of the 0+, T = 1 state of 6Li. For a neutral-current-induced weak pion amplitude equal to the "best" value given by Desplanques, Donoghue, and Holstein, the o. width is 1.3&10 eV.There is no contribution in lowest order from the intrinsic parity impurity in the u particle, but there is a small contribution from the deuteron.NUCLEAR STRUCTURE 6Li. Calculation of parity-violating o. decay of 0+, T = 1 state.Purely hadronic parity violation is experimentally well established'

Parity-violating α-decay of the 3.56 MeV Jπ, T = 0+, 1 state of 6Li

“…This is obviously the consequence of some kind of cancellations taking place in the matrix element. These strong cancellations appear to be a warning that it is dangerous to generate bound and scattering states inconsistently from different models, as has been done in [12] and [13]. A similar sensitivity is found in the modelling of the beta-delayed deuteron emission process in 6 He [21].…”

“…Finally, we compare our results with the predictions of [12] and [13]. In these models the pionic term alone gives 1.3 • 10 −8 eV and 1.1 • 10 −11 eV, respectively, using the DDH best value for the coupling constant.…”

“…The best experimental upper limit for the parity-violating α + d partial decay width is Γ ≤ 6.5 • 10 −7 eV [11]. The two most comprehensive theoretical descriptions of this process are based on the shell model [12] and the harmonic oscillator cluster model [13], respectively. If one assumes the same parameters for the parity-violating N-N potential, these two studies find parity-violating decay widths which differ by orders of magnitude.…”

“…Note that the initial state has a spatially extended halo-like neutron-proton tail [14]. The ability of the shell model [12] to reproduce such a loosely bound state with genuine three-body (α + p + n) nature is questionable. A model which cannot reproduce this tail tends to compress the wave function inside, thus supposedly increasing the decay width.…”

“…A model which cannot reproduce this tail tends to compress the wave function inside, thus supposedly increasing the decay width. Moreover, both studies [12,13] use a potential model for the α + d scattering, which is inconsistent with the description of the bound state.…”