Observation of Top Quark Production in Proton-Nucleus Collisions - Sirunyan, AM; Turnasyan, A; Adam, W; Arribrogi, F; Asilar, E; Bergauer, T; Brandstetter, J; Brondolin, E; Dragicevic, M; Ero, J; Del, Valle AE; Flechl, M; et al. (Physical Review Letters, 2017)