  In experiments searching for neutrinoless double-beta decay, the possibility
of identifying the two emitted electrons is a powerful tool in rejecting
background events and therefore improving the overall sensitivity of the
experiment. In this paper we present the first measurement of the efficiency of
a cut based on the different event signatures of double and single electron
tracks, using the data of the NEXT-White detector, the first detector of the
NEXT experiment operating underground. Using a \TO\ calibration source to
produce signal-like and background-like events with energies near 1.6 MeV, a
signal efficiency of $71.6 \pm 1.5_{\textrm{ stat}} \pm 0.3_{\textrm{ sys}} \%$
for a background acceptance of $20.6 \pm 0.4_{\textrm{ stat}} \pm 0.3_{\textrm{
sys}} \%$ is found, in good agreement with Monte Carlo simulations. An
extrapolation to the energy region of the neutrinoless double beta decay by
means of Monte Carlo simulations is also carried out, and the results obtained
show an improvement in background rejection over those obtained at lower
energies.
