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

Abstract

Background: 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. 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, driven by technological advances in microcalorimetry. Recent theoretical analyses offer reassurance that there are no significant theoretical uncertainties.Purpose: 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. Method:The shakeup and shakeoff theory of Carlson and Nestor is used as a basis for estimating the population of double-vacancy states.Results: A spectrum of satellites associated with each primary vacancy created by electron capture is presented. Conclusions: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. The spectrum shape is presently not well enough understood to permit a sensitive determination of the neutrino mass in this way.

Light sterile neutrino sensitivity of 163Ho experiments

“…The role of higher order excitations has been recently studied in refs. [110][111][112][113]. There is still not a good agreement among the different authors on the expected structures in the 163 Ho spectrum due to these excitations.…”

Ab initio calculation of the calorimetric electron-capture spectrum of Ho163 : Intra-atomic decay into bound states

“…The theoretical line-shape of the the differential electron capture nuclear decay rate in 163 Ho has been calculated before using different theoretical levels of complexity [6][7][8][9][10][11]13]. It was concluded by Robertson [9] that with the level of theory presented at that time "the spectrum shape is not understood well enough to permit a sensitive determination of the neutrino mass in this way".…”

“…Previous theoretical studies discussed the importance of spectral shake-up and shake-off features [6][7][8][9][10][11]. These calculations show that an even further improved description of the EC spectrum is necessary to explain the experimental data available at that time [12].…”

Warm Dark Matter Sterile Neutrinos in Electron Capture and Beta Decay Spectra

“…The reason is that for the shells above the vacancy the effective charge is closer to the one in the parent atom (there is one proton less in the nucleus but also one electron less in an inner shell) and therefore its binding energies should be used [34].…”

“…The contributions to the spectrum of the two-hole excitations that are actually distinct from the one-hole excitations (Eqs. (9) and (10)) have been a subject of recent studies devoted to search for the electron neutrino mass, and are therefore focused on the endpoint of the spectrum (see for instance [34][35][36]). For heavy neutrino searches a similar analysis should be performed at other regions of the energy spectrum, not just at the endpoint.…”