 Measurement of  x E  (Fig. 4) Assorted correlations between a fixed high-p T trigger hadron (  p Ttrig  =4.7GeV/c) and lower p T associated hadrons are used: the number of associated hadrons per trigger hadron is plotted as a function of x E. We fit to get  x E  for each given p Ttrigg.  Measurement of  z  (Fig. 5) If D(z)~exp(-z/  z  ) is the fragmentation function and f q (p qT ) is the parton final state transverse momentum distribution But x E ·z trigg =z, so The shape of the parton spectrum f q (p Tq ) is obtained by numerical Integration from the  0 spectra measured by PHENIX: A numerical iterative procedure is used to solve the last two equations for  z  and its errors.  Measurement of jet shape parameters  |j Ty |  and  |k Ty |  By fitting correlation functions like those in Fig. 2, we obtain the near/far angle widths presented in the left panels of Fig. 6. They are used then to calculate  |j Ty |  and  z   |k Ty | , which are presented in the right panels of Fig. 6. Finally,  z  from Fig. 5 is used to extract  |k Ty |  presented in Fig. 7. A comparison with existing data on  |k Ty |  in pp is shown in Fig. 8.  The following jet shape parameters have been measured by PHENIX in pp collisions:  |j Ty |  =359  11MeV/c  z   |k Ty |  =673  48MeV/c  |k Ty |  = 964  49MeV/c  They are in very good agreement with existing data;  The AuAu  |j Ty |  shows a very weak centrality dependence;  The AuAu  |k Ty |  on the other hand has a significant increase with centrality.  Jet shape parameters in dAu collisions have been also extracted by PHENIX collaboration - see posters by N.C.Grau, J. Jia, and W.G.Holzmann. The two-step method of deconvolution of the quadrupole and dijet terms described above was applied on assorted AuAu correlation functions for trigger charged hadrons with 3<p Ttrigg <5GeV/c and associated charged hadrons with 1.5<p T <3GeV/c. The centrality dependence of the extracted widths is presented in Fig. 9, while Fig. 10 presents the centrality dependence of the jet shape parameters  |j Ty |  and  z   |k Ty |  calculated from these widths.  Extracting jet shape parameters from AuAu correlation functions is more difficult because of the presence of the quadrupole term combined with the broadness of the dijet (far angle) term: as  F broadens, the dijet term resembles more with the quadrupole term. The following technique has been developed in order to disentangle the far-angle Gaussian width from the quadrupole oscillation:  The correlation function is fitted with the constraint that its amplitude at minimum is only given by quadrupole term. Extensive simulations with correlation functions of various shapes show, as expected, that the Gaussian widths are correctly recovered only when they are less than ~0.6rad, otherwise they are returned systematically lower. However, the quadrupole coefficient v 2 is always retrieved with very good accuracy.  The quadrupole coefficient v 2 is fixed to the value found above and the correlation function is fitted again, but this time the before mentioned constraint is dropped. Systematic errors are assigned to all jet shape parameters by varying v 2 within its errors from first step. See poster by N. N. Ajitannand for a more complex implementation of a similar technique. Deconvolution of quadrupole and dijet terms in AuAu correlation functions RESULTS – pp collisions Results – AuAu collisions Conclusions Jet Shape Measurements via Two-Particle Azimuthal Correlations in pp and AuAu collisions at Paul Constantin (Iowa State University) for the PHENIX Collaboration Quark Matter 2004 January 11-18, 2004 Two-Particle Azimuthal Correlation Functions  Charged Hadron Tracking (Fig.1): tracks are defined using the vertex detectors (BBC), the Drift Chambers (DC), and the first Pad Chamber (PC1). Then, background from conversion electrons, decays and albedo is efficiently reduced with a Ring Imaging Cerenkov (RICH) veto and a PC3 tight association cut.  Correlation Functions (Fig.2) with Mixed Event Technique:  Fit Function contains a monojet term (Gaussian at  =0), a dijet term (Gaussian at  =  ), and a quadrupole term:  Normalization: so, there are 5 free parameters: harmonic coefficient v 2, near/far angle Gaussian areas Y N /Y F, and near/far angle Gaussian widths  N /  F. Of course, in pp collisions v 2  0.  Jet Shape Parameters are calculated from the Gaussian widths (see below)  Jet Yields are calculated from the Gaussian areas: the number of associated hadrons per trigger hadron is 11 22 Fig.1 PHENIX Central Arms (beam view) Fig. 2 pp correlation functions: (a) 2<p T <2.5GeV/c, (b)3<p T <4GeV/c Jet Shape Parameters  Parameters defined with respect to jet axis (partonic momentum):  Parameters defined with respect to trigger:  Assuming Gaussian azimuthal distributions: Fig. 3 Diagram of a dijet event Fragment’s momentum fraction along jet axis Fragment’s momentum transverse to jet axis Fragment’s momentum out of (trigg,beam) plane  1D Component of Jet Fragmentation Transverse Momentum:  1D Component of Parton Intrinsic Transverse Momentum: Fig. 9 Near angle (top) and far angle (bottom) widths in AuAu collisions. Red bands are the corresponding pp values. Fig. 10  |j Ty |  (top) and  z  |k Ty |  (bottom) in AuAu collisions. Red bands are the corresponding pp values. Fig. 6 Near/far angle widths (left) and jet shape parameters (right) in pp collisions. Fig. 7 Extracted  |k Ty |  dependence on p T in pp collisions. Fig. 8 Comparison with world data on  |k Ty |  PHENIX Preliminary Fig. 5  z  dependence on p T PHENIX Preliminary Fig. 4 x E distributions for hadrons in 2-2.5GeV/c (open circles), 2.5-3GeV/c (squares), 3-4GeV/c (open squares) and 4-6GeV/c (triangles) PHENIX Preliminary