Test of NRQCD with Quarkonium Production in Jets at the LHC

Jet substructure provides us with a new way of probing the mechanisms of quarkonium production. We study quarkonium production within jets based on the fragmenting jet function (FJF) which describes the distribution of a quarknium in a jet with certain jet shape. FJF incorporates quarkonium fragmentation functions which can be obtained using NRQCD factorization formalism. Thus, the study of quarkonium production in jets also provides a test of NRQCD. To test our framework, we first investigated electron positron collisions where we have a good control of analytic calculations. Then the analysis was generalized to proton proton collisions and compared to recent LHCb data. We found that long distance matrix elements (which are the only inputs of NRQCD fragmentation functions) extracted at high pT gave better descriptions of the LHCb data than the ones from a global fit. We also did Monte Carlo analyses and found that the existing event generators were not sufficient. We attempted some modifications (of PYTHIA) and they agreed with our analytic calculations.