Speaker
Description
The NEXT experiment aims to conduct a sensitive search of the neutrinoless
double beta decay (ββ0ν) in $^{136}$Xe, using high-pressure gas electroluminescent
time projection chambers (HP-ELTPCs). The NEXT-White detector, a first
radiopure demonstrator, was operated between 2016 and 2021 in the Canfranc
Underground Laboratory (LSC). This detector demonstrated the capabilities
of the HP-ELTPC technology by providing a measurement of the two-neutrino
mode of the ββ decay, as well as a ββ0ν half-life limit of 1.3 × 10$^{24}$ yr at 90%
C.L., using a fiducial mass of only 3.50±0.01 kg of $^{136}$Xe. Following the decom-
missioning of NEXT-White, the NEXT-100 detector, which can hold up to ∼100
kg of Xe at 15 bar, started operation in 2024 at the LSC. The goal of NEXT-
100 is to prove the scalability of the NEXT technology and to provide the first
competitive results on the ββ0ν search. After a successful commissioning stage,
the detector has been calibrated with low ($^{83m}$Kr) and high energy ($^{228}$Th)
sources, reaching an energy resolution of below 1% FWHM at the Q$_{ββ}$ value
(2.46 MeV), which meets the experimental target. A first low-background run
has followed to measure and characterize the different background sources using
$^{136}$Xe-depleted xenon. In particular, the impact of the internal radon-induced
background has been demostrated to be negligible, with an index of ∼0.4×10$^{-4}$
counts/keV/kg/year. Thanks to the radon abatement system of the LSC, it has
been also proven that NEXT-100 operates in a virtually radon-free environment.
With an expected total background index below 10$^{-3}$ counts/keV/kg/year, this
detector is projected to reach a sensitivity of 6×10$^{25}$ yr at 90% C.L. after 3
years of data collection with $^{136}$Xe-enriched xenon. Furthermore, NEXT-100
will lay the groundwork for the construction of a ton-scale detector, boosting
the sensitivity above 10$^{27}$ yr and establishing the $^{136}$Xe HP-ELTPCs as major
players in the quest for the discovery of the ββ0ν decay.