Observation of a narrow mass state decaying into Upsilon(1S) + gamma in ppbar collisions at sqrt(s) = 1.96 TeV

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Using data corresponding to an integrated luminosity of 1.3 fb-1, we observe a narrow mass state decaying into Upsilon(1S)+gamma, where the Upsilon(1S) meson is detected by its decay into a pair of oppositely charged muons, and the photon is identified through its conversion into an electron-positron pair. The significance of this observation is 5.6 standard deviations. The mass of the state is centered at 10.551 ± 0.014 (stat.) ± 0.017 (syst.) GeV/c², which is consistent with that of the state recently observed by the ATLAS Collaboration.