Measurements of the production of P-wave charmonium states through radiative decays at the ATLAS experiment

The production cross sections of the χc1 and χc2 charmonium states are measured in pp collisions at √s = 7 TeV using 4.5 fb−1 of integrated luminosity recorded by the ATLAS detector at the LHC. The χc states are reconstructed via the radiative decay χc → J/ψ(μ+μ−)γ, where the photons are reconstructed using γ → e+ e− conversion in the detector material. Differential production cross sections for prompt and non-prompt χc1,2 are presented, as well as the fraction of inclusive J/ψ produced by feed-down from the χc states. The results are compared with a range of theoretical predictions. The branching fraction of ℬ (B+ → χc1K+) is measured using the same dataset and χc event selection