Fragmentation Properties Of Jets Produced In Pp Collisions At Square Root Sign S PDF Download

Two particle azimuthal correlation functions measured in pp and AuAu collisions at [square root of s subscript NN] = 200 GeV at midrapidity with the central arms of the PHENIX detector are analyzed in order to extract the properties of hadronic jets produced in QCD vacuum and highly excited QCD media, like the jet shape parameters j[Subscript T] and k[Subscript T], the jet conditional yields (number of associated hadrons per high p[Subscript T] trigger hadron), and the jet fragmentation function. The analysis of pp data starts with the measurement of the vacuum fragmentation function from which the p[Subscript T] dependence of the mean fragmentation momentum fraction z is extracted. We obtain a constant value of z = 0.74±0.02 for p[Subscript T] above 3 GeV/c. Soft (non-perturbative) parton fragmentation becomes significant below 3 GeV/c and the slope of the fragmentation function is p[Subscript T] dependent in this region. Gaussian fits to jet induced azimuthal correlations are employed to measure the mean jet fragmentation transverse momentum j[Subscript Ty] = 359 ± 11 (stat) ± 6 (syst) MeV/c and the mean partonic transverse momentum k[Subscript Ty] = 964 ± 49 (stat) ± 16 (syst) MeV/c. The analysis of AuAu data is based on azimuthal correlation functions between charged hadrons in the 1.5-3 GeV/c and 3-5 GeV/c p[Subscript T] regions in five classes of collision centrality. The mean jet fragmentation transverse momentum j[Subscript Ty] is centrality independent and consistent with the value in pp data mentioned above. A strong broadening with the centrality of the extracted mean partonic transverse momentum k[Subscript Ty] (multiplied by z[Subscript trigg]) is observed. This is an important finding because hadronic jet quenching through energy loss is expected to be accompanied by a broadening effect. Another important finding is that the jet conditional yields in both the near (delta phi [Difference] 0) and away (delta phi [Difference] pi) regions exhibit a slightly raising trend with centrality. This was also expected to accompany the jet quenching found at higher p[Subscript T] based on simple energy conservation considerations.