Observation of a New <em>χ_b</em> State in Radiative Transitions to Υ(1<em>S</em>) and Υ(2<em>S</em>) at ATLAS

The χb(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider at s√=7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb−1, these states are reconstructed through their radiative decays to Υ(1S,2S) with Υ→μ+μ−. In addition to the mass peaks corresponding to the decay modes χb(1P,2P)→Υ(1S)γ, a new structure centered at a mass of 10.530±0.005(stat)±0.009(syst) GeV is also observed, in both the Υ(1S)γ and Υ(2S)γ decay modes. This structure is interpreted as the χb(3P) system