Abstract
Background: The Gamow-Teller response of is important for the use of liquid argon as a medium for neutrino detection. An ambiguity about the Gamow-Teller strength for the excitation of states at 2290 and 2730 keV in results in a significant uncertainty for neutrino capture rates. This ambiguity is caused by the large discrepancy observed between strengths extracted from (, ) charge-exchange data and the transition strengths for the analog transitions studied in the decay of .
Purpose: This study was aimed at resolving the ambiguity between the results from the (, ) charge-exchange and -decay data.
Method: Shell-model calculations in the shell with a new interaction (WBMB-C) were used to study differences between the structure of the transitions from and . Distorted-wave Born approximation reaction calculations were used to investigate uncertainties in the extraction of Gamow-Teller strength from the (, ) data. New high-resolution data for the (,) reaction were used to gain further insight into the charge-exchange reaction mechanism and to provide more information to test the validity of the shell-model calculations.
Results: The shell-model calculations showed that interference between amplitudes associated with and components to the low-lying Gamow-Teller transitions, in combination with a difference in Coulomb energy shifts for and , can produce the differences on the scale of those observed between the charge-exchange and -decay data. In combination with the difference in nuclear penetrability of the (, ) and (,) probes, the different contributions from amplitudes associated with transitions in the and shells are likely also responsible for the observed discrepancy between the ratio of the cross sections for the low-lying states in the (, ) and (,) data.
Conclusions: On the basis of this study, it is recommended to use Gamow-Teller strengths extracted from the (, ) data, not the -decay data, for the calculation of neutrino capture rates. Further theoretical studies are required to achieve a consistent quantitative description for the energy differences between low-lying states in and and the experimentally observed Gamow-Teller strengths.
- Received 26 January 2014
- Revised 18 May 2014
DOI:https://doi.org/10.1103/PhysRevC.89.064313
©2014 American Physical Society