  The NEXT experiment aims to observe the neutrinoless double beta decay of
xenon in a high-pressure Xe136 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 Qbb. 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 Na22 1275 keV gammas and
electron-positron pairs produced by conversions of gammas from the Th228 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.
