Examination of the calorimetric spectrum to determine the neutrino mass in low-energy electron capture decay

Abstract

The standard kinematic method for determining neutrino mass from the beta decay of tritium or other isotope is to measure the shape of the electron spectrum near the endpoint. It has been known for 30 years that a similar distortion of the "visible energy" remaining after electron capture is caused by neutrino mass. There has been a resurgence of interest in using this method with 163-Ho. Recent theoretical analyses offer reassurance that there are no significant theoretical uncertainties. We show that the situation is, however, more complicated, and that the spectrum shape is presently not well enough understood to permit a sensitive determination of the neutrino mass in this way. The theoretical analyses consider only single vacancy states in the daughter 163-Dy atom. It is necessary to consider configurations with more than one vacancy that can be populated owing to the change in nuclear charge. The shakeup and shakeoff theory of Carlson and Nestor is used as a basis for estimating the population of double-vacancy states. A spectrum of satellites associated with each primary vacancy created by electron capture is presented. The theory of the calorimetric spectrum is more complicated than has been described heretofore. There are numerous shakeup and shakeoff satellites present across the spectrum, and some may be very near the endpoint.