A measurement of jet substructure variables in prompt J/\psi events with the ATLAS detector at $\sqrt{s}=$ 8 TeV

There are many open questions regarding charmonium production at hadron colliders. In order to describe the $p_T$ spectrum of prompt J/$\psi$ particles, the color octet mechanism from non-relativistic QCD (NRQCD) must be introduced. Color octet states have a net color charge which is expected to enhance hadronic activity around the J/$\psi$. Recently it has been suggested that jet substructure techniques may be able to discriminate between the the octet and singlet production mechanisms. Simulations of of N-subjettiness and the J/$\psi$-jet momentum fraction indicate the ability to separate the two production mechanisms. This work presents the first measurement of these variables (N-subjettiness, $\Delta R$ and jet-momentum fraction $z$) in $pp$ collisions at $\sqrt{s}=8~\text{TeV}$ with the ATLAS detector.