First proof of topological signature in the high pressure xenon gas TPC with electroluminescence amplification for the NEXT experiment

The NEXT experiment aims to observe the neutrinoless double beta decay of ¹³⁶Xe in a high-pressure xenon gas TPC using electroluminescence (EL) to amplify the signal from ionization. One of the main advantages of this technology is the possibility to reconstruct the topology of events with energies close to Q_ββ. This paper presents the first demonstration that the topology provides extra handles to reject background events using data obtained with the NEXT-DEMO prototype. Single electrons resulting from the interactions of ²²Na 1275 keV gammas and electronpositron pairs produced by conversions of gammas from the ²²⁸Th decay chain were used to represent the background and the signal in a double beta decay. These data were used to develop algorithms for the reconstruction of tracks and the identification of the energy deposited at the end-points, providing an extra background rejection factor of 24.3 ± 1.4 (stat.)%, while maintaining an efficiency of 66.7 ± 1.% for signal events.[Figure not available: see fulltext.]