Demonstration of Sub-Percent Energy Resolution in the NEXT-100 Detector

TL;DR

The NEXT-100 detector achieved a sub-percent energy resolution at 2615 keV, demonstrating its potential for precise measurements in neutrinoless double-beta decay searches, with a resolution extrapolated to 0.93% at the decay endpoint.

Contribution

This paper reports the first high-energy calibration of the NEXT-100 detector, achieving a near 0.9% FWHM energy resolution at 2615 keV, confirming its suitability for neutrinoless double-beta decay detection.

Findings

Energy resolution of (0.90 ± 0.02)% FWHM at 2615 keV

Linear response of the detector across calibration energies

Extrapolated resolution of 0.93% at Qββ (2458 keV)

Abstract

NEXT-100 is a high-pressure xenon time projection chamber with electroluminescent amplification, designed to operate with up to approximately 70.5 kg at 13.5 bar. It is the most recent detector developed by the NEXT collaboration to search for the neutrinoless double-beta decay ($\beta\beta 0\nu$) of Xe-136. The NEXT gas TPC technology offers the best energy resolution near the Q-value of the decay ($Q_{\beta\beta}$ = 2458 keV) among xenon detectors, which is set by design to be <1% FWHM. We report here the high-energy calibration of the detector using a Th-228 source, demonstrating linear response and an energy resolution of $(0.90 \pm 0.02)$% FWHM at the Tl-208 photopeak (2615 keV). This performance extrapolates to a resolution at the double-beta decay end-point of $R(Q_{\beta\beta})$ = $(0.93 \pm 0.02)$% FWHM, confirming the detector's capability for precision energy measurement in the search for $\beta\beta 0\nu$.