Comparison of the detector response and calibration function of metallic microcalorimeters for X-ray photons and external electrons

TL;DR

This paper investigates the response and calibration of metallic microcalorimeters for external electrons and X-ray photons, demonstrating their suitability for high-resolution spectroscopy of charged particles, with implications for neutrino mass experiments.

Contribution

It provides the first measurements of external electrons with MMCs and compares their response to X-ray signals, expanding the understanding of MMC performance for charged particle detection.

Findings

MMC detectors show linear response to external electrons and X-ray photons

Calibration functions for electrons and photons are characterized and compared

Results support MMC suitability for high-resolution electron spectroscopy

Abstract

Metallic microcalorimeters (MMCs) are cryogenic single-particle detectors that rely on a calorimetric detection principle. Due to their excellent energy resolution, close-to-ideal linear detector response, fast signal rise time and the potential for \SI{100}{\%} quantum efficiency, MMCs outperform conventional detectors by several orders of magnitude in resolution. These attributes make them particularly interesting for a broad spectrum of applications, including a next-generation neutrino mass experiment based on the measurement of the tritium beta-decay spectrum, with an objective of achieving a sensitivity surpassing that of the pioneering KATRIN experiment. However, although MMCs have been used in measurements of photons and heavy ions with great success, no information is currently available on the interaction between MMCs and external light charged particles such as electrons. This work aims to provide such missing information and to demonstrate that MMC-based detectors are suitable for high-resolution spectroscopy of external electron sources. Particularly, we present the first-ever measurements of external electrons using a metallic microcalorimeter, comprehensively discuss the characteristics of the signal shape and the calibration function and give a direct comparison between well-defined conversion electron and X-ray photon signals from the same $^{83}$Rb/$^{83m}$Kr source.