Measurement of the 136Xe ββ2ν half-life with NEXT-White

Abstract

The NEXT (Neutrino Experiment with a Xenon TPC) collaboration aims at the sensitive search of the neutrino-less double beta decay (𝛽𝛽0𝜈) of 136Xe at the Laboratorio Subterraneo de Canfranc (LSC). The observation of such a lepton-number-violation process would prove the Majorana nature of neutrinos, providing also handles for an eventual measurement of the neutrino absolute mass. A first large-scale prototype of a high-pressure gas-Xenon electroluminescent TPC, NEXT- White, has been operating at the LSC since 2016. This 5-kg radiopure detector has already proven the outstanding performance of the NEXT technology in terms of the energy resolution (<1% FWHM at 2.6 MeV) and the topology-based background rejection. NEXT-White has also measured the relevant backgrounds for the 𝛽𝛽0𝜈 search using both 136Xe-depleted and 136Xe-enriched xenon. In this talk, the measurement of the half-life of the two neutrino mode of the double beta decay (𝛽𝛽2𝜈) will be presented. For this measurement, two novel techniques in the field have been used: 1) a Richardson-Lucy deconvolution to reconstruct the single and double electron tracks, boosting the background rejection, and 2) a direct subtraction of the 𝛽𝛽 backgrounds, measured with 136Xe-depleted data. These techniques allow for background-model dependent and background-model independent results, demonstrating the robustness of the 𝛽𝛽2𝜈 half-life measurement and the unique capabilities of NEXT. The physics program of NEXT-White will be completed in late 2021, when the construction of the NEXT-100 detector at the LSC starts. Holding 100 kg of 136Xe and with a background index below 5×10^−4 counts/keV/kg/year, this detector will perform the first competitive 𝛽𝛽0𝜈 search within the NEXT roadmap. As validated with NEXT-White, NEXT-100 will reach a sensitivity to the half-life of 6×10^25 y after 3 years of data taking, paving the way for future ton-scale phases.