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

Abstract : 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 TeV with the ATLAS detector at the LHC using 4.5 fb^-1 of integrated luminosity. The chi_c states are reconstructed through the radiative decay chi_c -> J/psi gamma (with J/psi -> mu+mu-) where photons are reconstructed from gamma -> 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 B(B+ -> chi_c1 K+) = (4.9 +/- 0.9 stat. +/- 0.6 syst.) * 10^-4 is measured with the same dataset and chi_c event selection.
Document type :
Journal articles

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### Citation

G. Aad, S. Albrand, J. Brown, Q. Buat, B. Clement, et al.. Measurement of $\chi_{c1}$ and $\chi_{c2}$ production with $\sqrt{s}$ = 7 TeV $pp$ collisions at ATLAS. Journal of High Energy Physics, Springer, 2014, 7, pp.154. ⟨10.1007/JHEP07(2014)154⟩. ⟨in2p3-00984965⟩

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