Measurement of χ_c1and χ_c2production with √s = 7 TeV pp collisions at ATLAS

The prompt and non-prompt production cross-sections for the χ_c1and χ_c2charmonium states are measured in pp collisions at √s = 7TeV with the ATLAS detector at the LHC using 4.5 fb⁻¹of integrated luminosity. The χ_cstates are reconstructed through the radiative decay χ_c→ J/ψγ (with J/ψ → μ⁺μ⁻) where photons are reconstructed from γ → e+e− conversions. The production rate of the χ_c2state relative to the χ_c1state is measured for prompt and non-prompt χ_cas a function of J/ψ transverse momentum. The prompt χ_ccross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ_cdecays. The fractions of χ_c1and χ_c2produced in b-hadron decays are also measured.