Charmonium production at ATLAS

Understanding of the production of P-wave charmonium states is a significant bottleneck in the understanding of charmonium production as a whole. Current theoretical calculations are limited in their ability to model the production and decay of these states. We present new measurements of the differential production cross-sections of the chi_c1 and chi_c2 spin charmonium states, extending upon previous measurements in precision, kinematic reach, and number of measurements. The relative production cross-sections of the chi_c states through prompt and non-prompt production modes are explored as a function of transverse momentum, as well as the fraction of the total J/psi production which occurs via chi_c feed-down. Prompt and non-prompt production cross-sections for psi(2S) are presented, in the decay mode J/psi pi pi, to help provide an accurate picture of charmonium production. A competitive measurement of the production cross-section of prompt J/psi mesons in association with a W boson is also presented. This process provides a powerful probe of the production mechanism of charmonium and is also sensitive to multiple parton interactions in the colliding protons. Results are compared with latest theoretical predictions from a variety of theoretical approaches.