A Measurement of the Radiation Environment Around Prompt J/ψ Events at ATLAS

The J/ψ particle has been the source of much research since its

discovery in 1974. It provides an important probe of quantum

chromodynamics and has lead to many important insights into the

interactions of quarks and gluons in bound states. The rate of J/ψ

production was found to be much higher than expected at hadron

colliding experiments. Non-relativistic quantum chromodynamics was

developed in order to address these issues. This theory predicts a

strong spin-alignment not observed in data. All previous measurements

of J/ψ production have overlooked the hadronic environment the

J/ψ is produced in. This work is the first exploration of the

radiation surrounding J/ψ events measured at ATLAS at

√s=8 TeV. This is the first measurement of the

separation between the J/ψ and a matched jet and the second

measurement of the momentum fraction shared between the jet and the

J/ψ. These variables probe the radiation environment around the

J/ψ, and provide a new ways to understand quarkonia production.