Sensitivity of the NEXT-100 detector to neutrinoless double beta decay

Abstract

A high pressure xenon gas time projection chamber with electroluminescent amplification (EL HPGXe TPC) searching for the neutrinoless double beta (0νββ) decay offers: excellent energy resolution [1, 2] (0.5 − 0.7% FWHM at the Qββ), by amplifying the ionization signal with electroluminescent light, and tracking capabilities [3], as demonstrated by the NEXT collaboration using two kg-scale prototypes. The NEXT collaboration is building an EL HPGXe TPC capable of holding 100 kg (NEXT-100) of xenon isotopically enriched in 136Xe. The installation and commissioning of the NEXT-100 detector at the Laboratorio Subterráneo de Canfranc (LSC) is planned for 2018. The current estimated background level for the NEXT-100 detector is of 4 × 10−4 counts/keV-kg-yr or less in the energy region of interest [4]. Assuming an energy resolution of 0.75% FWHM at the Qνββ and a 0νββ signal efficiency of about 28%, this gives an expected sensitivity (at 90% CL) to the 0νββ decay half life of yr for an exposure of 275 kg yr. A first phase of the NEXT experiment, called NEW, is currently being commissioned at the LSC. The NEW detector is a scale 1:2 in size (1:10 in mass) of the NEXT-100 detector using the same materials and photosensors and will be used to perform a characterization of the 0νββ backgrounds and a measurement of the standard double beta decay with neutrinos (2ν ββ). An 8 sigma significance for the 2νββ signal in the NEW detector has been estimated for a 100-day run.