Demonstration of the event identification capabilities of the NEXT-White detector

Abstract

In experiments searching for neutrinoless double-beta decay, the possibility of identifying the two emitted electrons is a powerful tool in rejecting background events and therefore improving the overall sensitivity of the experiment. In this paper we present the first measurement of the efficiency of a cut based on the different event signatures of double and single electron tracks, using the data of the NEXT-White detector, the first detector of the NEXT experiment operating underground. Using a 228 Th calibration source to produce signal-like and background-like events with energies near 1.6 MeV, a signal efficiency of 71.6 ± 1.5 stat ± 0.3 sys % for a background acceptance of 20.6 ± 0.4 stat ± 0.3 sys % is found, in good agreement with Monte Carlo simulations. An extrapolation to the energy region of the neutrinoless double beta decay by means of Monte Carlo simulations is also carried out, and the results obtained show an improvement in background rejection over those obtained at lower energies.

Results and future plans of the NEXT double beta decay experiment

“…NEXT A. Laing possible to benchmark the topological rejection factors expected in a data-driven manner. In [3], the rejection power was shown to be in good agreement with the Monte Carlo expectations and to select ∼71% of signal-like events while rejecting ∼80% of the single electron tracks. There are currently data from two main low-background runs on disk.…”

“…The technology was first demonstrated with kg-scale detectors [1,2] and is currently being exploited at a larger scale by the Next-White detector at Laboratorio Subterráneo de Canfranc (LSC) [3,4,5]. A rich scientific program is currently developing the next stage detector (Next-100) while looking to the future with multiple R&D efforts for a tonne-scale NEXT.…”

Demonstration of background rejection using deep convolutional neural networks in the NEXT experiment

“…The NEXT (Neutrino Experiment with a Xenon TPC) experiment is searching for neutrinoless double-beta decay (0νββ) in 136 Xe at the Laboratorio Subterráneo de Canfranc (LSC) in Spain. In the ongoing first phase of the experiment, the 5 kg-scale TPC NEXT-White [1] has demonstrated excellent energy resolution [2] and the ability to reconstruct high-energy (of the order of 2 MeV) ionization tracks and distinguish between the topological signatures of two-electron and one-electron tracks [3]. It has also been used to perform a detailed measurement of the background distribution and is expected to be capable of measuring the 2νββ mode in 136 Xe with 3.5σ sensitivity after 1 year of datataking [4].…”

Cosmogenic Activation in Double Beta Decay Experiments

“…Several prototypes (with mass of ∼1 kg) were designed and operated in a first step to demonstrate the advantages of the technology, including a distinctive signal topology and very good energy resolution [158,159]. As a second phase, the NEXT-White demonstrator (with 5 kg of xenon) was built in Canfranc [160] and in 2020 is running smoothly, having confirmed the background discrimination capability from the topological signature [161] and shown an energy resolution of 1% (FWHM) in the region of interest [162]; energy resolution, which depends on the stability of operation parameters, wave-shifters, light detectors, and other elements, is much better in xenon gas than in liquid because the fluctuations in the ionization production are smaller than the ones due to pure Poisson statistics (Fano factor is lower than 1 in gaseous phase). NEXT-100 (with 100 kg of xenon at 15 bar) is the next stage of the program [163], built with radiopure specifications [164] as a scale up of NEXT-White by 2:1 in size; operation might start in 2021.…”