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

P Ferrario,J Renner,D Lorca,A Goldschmidt,M Monserrate,L Labarga,F Monrabal,P Lebrun,T Miller,S Cebrián,J Rodríguez,V Álvarez,L M P Fernandes,D Shuman,J A Hernando Morata,A Marí,S Cárcel,Z Tsamalaidze,G Martínez-Lema,A Laing,N Yahlali,A Cervera,R Webb,L Ripoll,M Sorel,D González-Díaz,N López-March,C A O Henriques,C Sofka,A L Ferreira,G Luzón,A Para,H Yepes-Ramírez,J Martín-Albo,P Novella,M Nebot-Guinot,M Losada,I Liubarsky,R Esteve,J Torrent,C M B Monteiro,A Simón,J Muñoz Vidal,V M Gehman,M Querol,M Diesburg,J.f.c.a Veloso ,C.a.n Conde ,James T White ,Francisco Mora ,I.g Irastorza ,T Dafní ,A J Martínez ,D R Nygren ,F.p Santos ,J.m.f Dos Santos ,F.i.g.m Borges ,J M Hauptman ,J.f Toledo ,José L Pérez-Aparicio ,J.j Gómez-Cadenas ,L.m Moutinho ,Llorenç Serra ,C.d.r Azevedo ,Rafael Gutiérrez ,J.a Villar ,E.d.c Freitas ,Javier Laso Pérez ,Julio Pérez Díaz

doi:10.1007/jhep01(2016)104

Abstract

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.

Highlights

The experimental signature of a neutrinoless double beta decay are two electrons with total kinetic energy equal to Qββ
An example of single electron track candidate is shown in figure 6 and a typical example of double electron track candidate is shown in figure 7
The evaluation of the figure of merit was performed as a function of the blob candidate radius and the minimum energy required for the low energy blob candidate, using Monte Carlo (MC) data

Summary

Introduction

For this reason, to be able to make the measurement, an experiment must be optimised simultaneously for energy resolution and the rejection of non-signal events with energies similar to Qββ. The use of a topological particle identification based on the expected signature of a double electron (signal) event compared to that of a single electron (background) produced by the interaction of high energy gammas is presented here. Background events from single electrons, typically leave a single continuous track with only one blob (figure 1-right) The use of this topological signature to eliminate background in ββ0ν experiments was pioneered by the Caltech-Neuchatel-PSI Collaboration in the Gotthard Underground Laboratory [8], using a gaseous 136Xe TPC with multiwire read-out, with a fiducial mass of 3.3 kg of 136Xe at a pressure of 5 atm

Results

Discussion

Conclusion