Contribution of Subthreshold States to the Residual Energy Distribution of 159Dy
Abstract
We investigate the residual energy distribution in the electron capture (EC) process of 159Dy, emphasizing the role of subthreshold atomic states, which have typically been omitted in conventional spectral analyses. By incorporating these energetically forbidden hole states into the spectral function P(E), we demonstrate a significant enhancement - over an order of magnitude - in the EC rate near the zero-momentum neutrino emission region. This enhancement increases further with larger Q values, contrary to standard expectations. Our analysis shows that P(E) can be experimentally determined, resolving ambiguities near the endpoint and enabling new approaches to 'ultra-low Q value' EC reactions for neutrino mass studies.
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