Speaker
Description
Heavy quarkonium production can be described as perturbative heavy quark-antiquark pair production and nonperturbative hadronization. Studying quarkonium production inside jets provides insight into quarkonium evolution in the nonperturbative process, which can be characterized by the jet fragmentation fraction of the quarkonium transverse momentum with respect to the enclosing jet. LHCb initiated this kind of study and demonstrated that the description of higher-order parton showers is crucial in understanding these processes. This presentation will report the current status of quarkonium-in-jet studies in CMS. We present the measurement of 𝐽/𝜓 and Υ(nS) production in jets in PbPb collisions at 5.02 TeV per nucleon pair and pp collisions at 13.6 TeV, respectively. The measured jet fragmentation function is significantly shifted towards less than one, meaning that jet carries significantly more momentum. The results indicate that quarkonia are less isolated than what event generators predict. This provides important constraints on modelling the underlying event and parton shower in theory and simulations.
