The NEXT experiment. Towards phase I

Abstract

Phase I of the NEXT-100 $0\nu\beta\beta$ experiment (NEW) is scheduled for data taking in 2015 at Laboratorio Subterr\'aneo de Canfranc in the Spanish Pyrenees. Thanks to the light proportional technique, NEW anticipates an outstanding energy resolution nearing the Fano factor in Xenon (0.5-1%FWHM@$Q_{\beta\beta,^{136}Xe}$), with a TPC-design that allows tracking and identification of the double end-blob feature of the $0\nu\beta\beta$ decay. When properly mastered, the combination of these two assets can suppress the irreducible $2\nu\beta\beta$ and (single-blob) $\gamma$ backgrounds from natural radioactivity to minute levels, of the order of $5\times{10^{-4}}$ ckky. Given our knowledge of the available phase-space as obtained from neutrino oscillation experiments, this feat will expectedly allow for a sensitivity to the effective electron neutrino mass of $m_{\beta\beta}\simeq 30$ meV for exposures at the 20 ton $\times$ year scale. Hence, ultimately, a full survey of the inverse hierarchy of the neutrino mass ordering appears to be within reach for a ton-scale experiment based on this technology. NEW, with 10 kg of Xenon 90%-enriched in $^{136}$Xe, sets an unprecedented scale for gaseous Xenon TPCs and will be an important milestone for its anticipated upgrades (100 kg and 1 ton). I briefly summarize the status of the NEXT experiment, from the main results obtained with $\sim 1$ kg prototypes that substantiate the concept, to the ongoing works for deploying its first phase.