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Description
The NEXT experiment aims to conduct a sensitive search of the neutrinoless double beta decay ($\beta\beta0\nu$) 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 $\beta\beta$ decay, as well as a $\beta\beta0\nu$ half-life limit of $1.3\times10^{24}$ yr at 90\% C.L., using a fiducial mass of only 3.50$\pm$0.01 kg of $^{136}$Xe. Following the decommissioning of NEXT-White, the NEXT-100 detector, which can hold up to $\sim$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 $\beta\beta0\nu$ 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$_{\beta\beta}$ 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 $\sim$0.4$\times$10$^{-4}$ counts/keV/kg/year. Thanks to the Rn abatement system of the LSC, it has been also proven that NEXT-100 operates in a virtually Rn-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$\times$10$^{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 $\beta\beta0\nu$ decay.