First results of the NEXT-100 detector using $^{83m}$Kr decays

TL;DR

The paper reports initial results from the NEXT-100 detector using $^{83m}$Kr decays, demonstrating excellent energy resolution and stability, which are promising for future double beta decay searches with xenon gas detectors.

Contribution

This work presents the first calibration and performance results of the NEXT-100 detector using $^{83m}$Kr, showing energy resolution comparable to previous detectors and promising extrapolation to the target energy.

Findings

Energy resolution of 4.37% FWHM at 41.5 keV

Fiducial energy resolution of 4.16% FWHM at 10 bar

Projected energy resolution near 0.5% FWHM at $Q_{\beta\beta}$

Abstract

The NEXT collaboration is investigating the double beta decay of $^{136}$Xe using high-pressure gas electroluminescent time projection chambers, which provide excellent energy resolution together with a robust topological signature. Operating at the Laboratorio Subterr\'aneo de Canfranc (LSC) and building on the success of the NEXT-White detector, the NEXT-100 apparatus began commissioning in May 2024 and started operation with xenon at a pressure of 4 bar in October 2024. We report here the first results obtained with NEXT-100 using low-energy calibration data from $^{83m}$Kr decays, which allow mapping of the detector response in the active volume and monitoring of its stability over time. After homogenizing the light response, we achieve an energy resolution of 4.37% FWHM at 41.5 keV for $^{83m}$Kr point-like energy deposits contained in a radius of 425 mm. In a fiducial region representing the operating conditions of NEXT-100 at 10 bar we obtain an improved energy resolution of 4.16% FWHM. These results are in good agreement with that obtained in NEXT-White, and an $E^{-1/2}$ extrapolation to $Q_{\beta\beta}$ yields an energy resolution close to 0.5% FWHM, well below the 1% FWHM design target.