Quenching of gA deduced from the β-spectrum shape of 113Cd measured with the COBRA experiment

Abstract

A dedicated study of the quenching of the weak axial-vector coupling strength gA in nuclear processes has been performed by the COBRA collaboration. This investigation is driven by nuclear model calculations which show that the β-spectrum shape of the fourfold forbidden non-unique decay of 113Cd strongly depends on the effective value of gA. Using an array of CdZnTe semiconductor detectors, 45 independent 113Cd spectra were obtained and interpreted in the context of three nuclear models. The resulting effective mean values are g‾A(ISM)=0.915±0.007, g‾A(MQPM)=0.911±0.013 and g‾A(IBFM-2)=0.955±0.022. These values agree well within the determined uncertainties and deviate significantly from the free value of gA. This can be seen as a first step towards answering the long-standing question regarding quenching effects related to gA in low-energy nuclear processes. Keywords: 113Cd beta-decay, Axial-vector coupling, gA quenching, Spectrum-shape method, CdZnTe, COBRA