Measurement of $\chi_{c1}$ and $\chi_{c2}$ production with $\sqrt{s}=7\,\mathrm{TeV}$ $pp$ collisions at ATLAS

The prompt and non-prompt production cross sections for the $\chi_{c1}$ and $\chi_{c2}$ charmonium states are measured in $pp$ collisions at $\sqrt{s}=7\,\mathrm{TeV}$ with the ATLAS detector at the LHC using $4.5\,\mathrm{fb}^{-1}$ of integrated luminosity. The $\chi_{c}$ states are reconstructed through the radiative decay $\chi_{c}\rightarrow J\psi\,\gamma$ (with $J/\psi\rightarrow\mu^{+}\mu^{-}$) where photons are reconstructed from $\gamma\rightarrow e^{+}e^{-}$ conversions. The production rate of the $\chi_{c2}$ state relative to the $\chi_{c1}$ state is measured for prompt and non-prompt $\chi_{c}$ as a function of $J/\psi$ transverse momentum. The prompt $\chi_{c}$ cross sections are combined with existing measurements of prompt $J/\psi$ production to derive the fraction of prompt $J/\psi$ produced in feed-down from $\chi_{c}$ decays. The fractions of $\chi_{c1}$ and $\chi_{c2}$ produced in $b$-hadron decays are also measured. In addition to measurements of inclusive $\chi_{c}$ production, the branching fraction ${\cal B}(B^{\pm}\to\chi_{c1} K^{\pm}) = (4.8 \pm 0.6\,\mathrm{(stat.)} \pm 0.6 \,\mathrm{(syst.)})\times 10^{-4}$ is also measured with the same dataset and $\chi_{c}$ event selection.