Sources of multiple K-GS components and their broadening

Ascertain the mechanisms that generate multiple components and the excess broadening of the K-capture to 7Li ground-state (K-GS) peak in the 7Be electron-capture recoil spectrum recorded with tantalum-based superconducting tunnel junction detectors, and quantitatively characterize their contributions beyond chemical shifts and instrumental resolution.

Background

The observed K-GS peak exhibits multiple components and a full width significantly exceeding the photon-resolution benchmark of the detectors. Chemical shifts of Li core levels in Ta account for only part of the width. The authors speculate that additional contributions, such as multi-electron shake-up involving Ta 5d electrons, may be relevant.

Clarifying the sources and magnitudes of these effects is necessary for an accurate physical model of the lineshape, which directly impacts background modeling in the sterile neutrino search.