Measurement of χ c 1 and χ c 2 production with s = 7 TeV pp collisions at ATLAS

The prompt and non-prompt production cross-sections for the χ c 1 and χ c 2 charmonium states are measured in pp collisions at s = 7 TeV with the ATLAS detector at the LHC using 4 . 5 fb −1 of integrated luminosity. The χ c states 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 c 2 state relative to the χ c 1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-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 c decays. The fractions of χ c 1 and χ c 2 produced in b -hadron decays are also measured.