We report results from the first search for νμ → νe transitions by the NOvA experiment. In an exposure
equivalent to 2.74 × 1020 protons on target in the upgraded NuMI beam at Fermilab, we observe 6 events in
the Far Detector, compared to a background expectation of 0.99 0.11ðsystÞ events based on the Near
Detector measurement. A secondary analysis observes 11 events with a background of 1.07 0.14ðsystÞ.
The 3.3σ excess of events observed in the primary analysis disfavors 0.1π < δCP < 0.5π in the inverted
mass hierarchy at the 90% C.L.