AnalogE1transitions and isospin mixing

Abstract

We investigate whether isospin mixing can be determined in a model-independent way from the relative strength of E1 transitions in mirror nuclei. The specific examples considered are the A = 31 and A = 35 mirror pairs, where a serious discrepancy between the strengths of 7/2 − → 5/2 + transitions in the respective mirror nuclei has been observed. A theoretical analysis of the problem suggests that it ought to be possible to disentangle the isospin mixing in the initial and final states given sufficient information on experimental matrix elements. With this in mind, we have obtained a lifetime for the relevant 7/2 − state in 31 S using the Doppler-shift attenuation method (DSAM). We have then collated the available information on matrix elements in order to examine the level of isospin mixing for both A = 31 and A = 35 mirror pairs.

One-proton and one-neutron knockout reactions from N=Z=28Ni56 to the A=55Spieker1, Gade2, Weißhaar3 et al. 2019Phys. Rev. CSelf Cite13070View full textAdd to dashboardCite

“…3), which suggests a similar structure of the 1/2 + state in the mirror pair and supports the hypothesis that the observed change in the E 1 decay pattern probes the degree of mixing between the two 3/2 − states. The amount of isospin mixing needed to explain the E 1 asymmetry for a low-lying 7/2 − level in the A = 35 and a 9/2 + stateintheA = 67 mirror nuclei was estimated to be on the order of 1-5% [4,[7][8][9]. In contrast to Refs.…”

“…In both cases the first E 1matrix element is also comparably large. We note that an E 1 transition between pure (2s 1/2 ) −1 (1 f 7/2 ) 8 hole and (1 f 7/2 ) 6 (2p 3/2 ) 1 particle configurations for the 1/2 + and 3/2 − , respectively, would be forbidden. Consequently, more complex configurations have to be present to explain the enhanced E 1 rates.…”

“…§ Present address: Lawrence Livermore National Laboratory, Livermore, California, 94550, USA. violation though the exact underlying mechanism is still discussed [8,9].…”

Isospin symmetry in the odd-odd mirror nuclei44V/44Sc

“…Despite the fact that isospin rules dictate that the B(E1) should be identical in mirror nuclei, some cases of strong asymmetries in B(E1) strengths have been indicated by recent data, especially in the A = 35 [34] and A = 31 [35] mirror pairs, and the factor of 40 here does not seem out of line. A summary of the current situation regarding these asymmetries is given by Pattabiraman et al [36] where factors ranging from 40 to 50 were also presented. For the nuclei presented in that work, the E1 transitions were weak (10 −6 or 10 −7 Wu) and the analysis showed that, at least in the case of A = 35, such weak transition strengths can be strongly perturbed in the presence of moderate isospin-mixing at the level of 1%, causing an asymmetry.…”

“…A beam of 36 Ar was accelerated to 95 MeV by the AT-LAS facility at Argonne National Laboratory. The beam nuclei impinged on a 0.25 mg/cm 2 10 B target to produce 46 V as a compound nucleus.…”