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Contribution of Subthreshold States to the Residual Energy Distribution of ^{159}Dy
Tadafumi Kishimoto1, Toru Sato1
1Osaka University, Research Center for Nuclear Physics, Ibaraki, Osaka 567-0047, Japan.
Abstract:
We investigate the residual energy distribution in the electron capture (EC) process of ^{159}Dy, 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 end point and enabling new approaches to "ultralow Q value" EC reactions for neutrino mass studies.
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