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

he production cross sections of the χc1 and χc2 charmonium states are\nmeasured in\npp collisions at √s = 7 TeV using 4.5 fb−1 of integrated luminosity\nrecorded by the\nATLAS detector at the LHC. The χc states are reconstructed in the radiative\ndecay\nχc → J/ψ(μ+μ−)γ, where the photons are reconstructed using γ → e+e−\nconversion\nin the detector material. Understanding of the P-wave charmonium states\nproduction is\ncrucial for understanding of the charmonium production as a whole. Besides\ndifferential\ncross section measurements of the prompt and non-prompt production of χc1,2\ndifferential\ncross section measurements, the relative production cross-sections of the χc\nstates through\nthe prompt and non-prompt production modes are measured, as well as the\nfraction of the\ntotal J/ψ production which occurs via the χc feed-down. Experimental\nanalysis is com-\npared with the latest theoretical predictions from a variety of theoretical\napproaches. As\na bonus, a branching fraction of B(B+ → χc1 K+) is measured using the same\ndataset and\nχc event selection.