  NOvA is a long-baseline accelerator-based neutrino oscillation experiment
that is optimized for $\nu_\mu\to\nu_e$ measurements. It uses the upgraded NuMI
beam from Fermilab and measures electron-neutrino appearance and muon-neutrino
disappearance at its Far Detector in Ash River, Minnesota. The $\nu_e$
appearance analysis at NOvA aims to resolve the neutrino mass hierarchy problem
and to constrain the CP-violating phase. The first data set of
$2.74\times10^{20}$ protons on target (POT) equivalent exposure taken by NOvA
has been analyzed. The first measurement of electron-neutrino appearance in
NOvA provides solid evidence of $\nu_\mu\to\nu_e$ oscillation with the NuMI
beam line. Electron-neutrino identification is the key ingredient for the
$\nu_e$ appearance analysis. The electron-identification algorithm used to
produce the primary results presented here compares 3-D shower-energy profiles
with Monte Carlo prototypes to construct likelihoods for each particle
hypothesis. Particle likelihoods, among other event-topology variables, are
used as inputs to an Artificial Neural Network for the final electron-neutrino
identification. The design and implementation of this algorithm is also
presented.
