Status of the NEXT experiment for neutrinoless double beta decay searches

Abstract

NEXT (Neutrino Experiment with a Xenon TPC) is a neutrinoless double beta decay experiment located at the Laboratorio Subterr\'aneo de Canfranc (LSC, Spain). Its aim is to demonstrate that the neutrino is a Majorana particle by detecting the neutrinoless double beta decay process in xenon gas enriched in the $^{136}$Xe isotope. The detector technology used in NEXT is that of radiopure high pressure time projection chambers with electroluminescence amplification, which provide excellent energy resolution better than 1$\%$ FWHM in the energy region of interest, topological reconstruction that allows rejecting single-electron background events and a strong potential for "in situ" tagging of the barium daughter ion. The experiment has been developing in phases. The NEXT-White detector has recently finished operation at the LSC and contained approximately an active Xe mass of 5 kg. Its purpose was to demonstrate the excellent energy resolution, to validate the reconstruction algorithms and the background model, and to make a measurement of the two-neutrino double beta decay of $^{136}$Xe. The 100 kg NEXT-100 detector is under construction and is scheduled to be installed and assembled by the first half of 2022. The predicted 90$\%$ CL sensitivity to the neutrinoless double beta decay half-life will reach $10^{26}$ years for an exposure of about 400 kg $\cdot$ year. A vigorous program towards the development of ton-scale detectors is also under way, including extensive R$\&$D towards the realization of in-situ Ba$^{2+}$ tagging as means to achieve virtually zero-background detection. A first module with a mass of at least 500 kg may be operating as early as 2026 at the LSC. In this manuscript, recent results obtained with the NEXT-White detector will be presented, as well as the NEXT-100 construction status and on the prospects of future NEXT detectors.