Splitting function in pp and PbPb collisions at 5.02 TeV

A measurement of the splitting function in pp and PbPb collisions at a center of mass energy of 5.02 TeV per nucleon pair is presented. The virtuality evolution of partons traversing the hot QCD medium created in a heavy ion collision is potentially modified due to interactions with the color charges of the medium. This measurement probes this phenomenon by measuring the generalized fragmentation function, or splitting function, over a wide range of jet transverse momentum and various collision centrality selections. The shared momentum fraction of two subjets resulting from a parton splitting is observed to be modified towards a more imbalanced fraction in central PbPb collisions compared to peripheral PbPb and pp collisions. In addition, the measurement in pp collisions is compared to the prediction of the splitting function from the {\tt PYTHIA} and {\tt HERWIG} event generators.