Measurement of the Shared Momentum Fraction zg using Jet Reconstruction in p + p and Au + Au Collisions with STAR

One key difference in current energy loss models lies in the treatment of the Altarelli-Parisi, AP, splitting functions. It has been shown that the shared momentum fraction, henceforth called Jet Splitting Function zg as determined by the SoftDrop grooming process can be made a Sudakov-safe measurement of the symmetrized AP functions in p+p collisions. The STAR collaboration presents the first zg measurements at sNN=200 GeV in p+p and Au+Au collisions, where in Au+Au we use a set of di-jets with hard cores reconstructed with a 2 GeV/c constituent cut. For a jet resolution parameter of R=0.4, these di-jet pairs were found to be significantly imbalanced with respect to p+p, yet regained balance when all soft constituents were included. We find that within uncertainties there are no signs of a modified Jet Splitting Function on trigger or recoil sides of this di-jet selection.