Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Angular Correlation Studies in PHENIX Wolf G. Holzmann for the Collaboration
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Jets: Flow: Primarily from gluons at RHIC Produced early in the collision Probe hot and dense media that they traverse Primarily from pressure build- up Produced early Reflect conditions in collision zone (energy density etc.) Why study azimuthal angular correlations ? Provides insights on Saturation Physics CGC: Correlation studies can provide information On the particle production mechanism, EOS, QGP formation …
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Features of Angular Correlation Functions (Distributions) Anisotropy ( ) Asymmetry ( ) Correlation functions or distributions can exhibit asymmetry & anisotropy The latter is mainly determined by the away side (> 90 deg) if you have an asymmetric shape.
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration How to extract relevant information from correlation Flow leads to strong anisotropy Hydro or Transport With large Opacity Saturation Model Mini-Jets, lead to strong anisotropy and an asymmetry Jets & Mini-Jets, lead to strong anisotropy and an asymmetry HIJING Very different mechanisms can account for similar observables Experimental challenge to disentangle them …
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Some of the approaches undertaken in PHENIX Various methods currently exploited in PHENIX: Angular Distributions with respect to a leading photon Two Particle Azimuthal Correlations with A) 2 particles from the same pT range (fixed pT correlations) B) 1 particle in a given reference pT range, the other particle outside in a different pT bin (assorted pT correlations) Three Particle Angular Correlations Cumulants Reaction Plane (not covered here, please see ShinIchi Esumi’s presentation) Different methods reveal different aspects of the correl. fctns. What can one learn from combining all of these analyses ? Well, relax, lean back and enjoy the ride …
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration trigger associated h incoming partons 00 Select events with a photon of pt > 2.5 GeV/c. Assumption: Mostly ’s from decay of a high pt (leading particle) Build distributions in delta -space of the charged hadrons relative to the trigger photons. Leading Photon Correlations PHENIX Preliminary raw differential yields 2-4 GeV black = pair distribution green = mixed event pair distribution purple = bkg subtracted distribution Task: Look at the relatively “clean” environment of p-p where we Think we know there are jets and relate this to Au-Au data …
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration P-PAu-Au Interestingly, the Au-Au shows many of the same features of pp. Thus being indicative of the presence of jets. P-P shows jet like features: strong near angle correlation broader and reduced away side Au-Au also shows jet like features strong near angle correlation broader and reduced away side Leading Correlations in p-p and Au-Au (*)
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Fit results of the jet-like amplitude Per Trigger quantification … In order to quantify the effect one can retrieve a “per trigger yield” (since one is actually looking at an angular distribution). Fit with pythia + cos(2phi) and look at the result. Observed effect can be well described by a fit to PYTHIA expect. and a harmonic ( cos(2phi) ) term. Within the errors (statistical only) no strong centrality dependence (*) (M. Chiu for the PHENIX Collaboration, QM2002 proceedings, nucl-ex/ ) (*)
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration What do angular correlation functions reveal in addition One observes asymmetries and anisotropies and can probe them The latter behave consistent with the idea of jet-like correlations One can further tighten the case by looking at the angular correlation functions and their characteristics pT “fixed” pT correlations 2 particles within the same bin Preliminary opp. charge small delta etasame charge large delta eta (P. Constantin, QM2002 poster)
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Near angle width vs pT j =400 MeV Again, the Au-Au data seems to follow the trend of the p-p, i.e. within the errors no apparent broadening as compared to p-p is observed. (P. Constantin, QM2002 poster) Jet topologies … jTjT Jet PTPT jTjT P out kTkT
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Another Approach: Three Particle Correlations p2 p3 geometric mean p1 =( x x ) 1/3 Since jets cluster in phase space and if the average jet multiplicity > 2 correlating three particles will enhance the jet signal over the background in regions were the signal is small. Jets:Flow: “bump” “dip” large near angle enhancement Jets and flow correlations look entirely different in this variable. Good way to disentangle the relative contributions of jets and flow
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX CollaborationHIJINGFLOW fit to data Centrality 30-60% HIJINGFLOW fit to data Data exhibits the same features For lower pT the data is fairly well described by a pure flow case, while at higher pT the data lies in between the cases of pure flow and HIJING (jet- dominated) thus indicating an admixture of both mechanisms. Provide additional information by comparing to 2 particle correlation Next step: Quantify the observed effect and compare to other methods used.
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Asymmetries vs Anisotropies pT (ref) pT “assorted” pT correlations 1 part within ref. bin the 2 nd part. out- side Asymmetry sensitive to the choice of reference pT range Anisotropy largely insensitive … Q: Can the anisotropies reveal additional information on jets? illustrative sketch assorted correlation functions PHENIX PRELIMINARY
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Strategy Need to establish a method of comparison between the v2 values of Au-Au and p-p (d-A). One way of testing this: - Establish a scaling relationship in Au-Au first, then compare to pp,dA - Use v2(pT)/v2(int) (scale the differential by the integral v2, Idea: account for centrality) -Compare to the other methods currently exploited
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Interestingly enough, the differential v2(pT) scales with the integral v2! Promising point to start from. Comparison with pp currently underway … not scaled v2(pT)scaled v2(pT)/v2_int Scaling in Au-Au
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration Conclusion and Outlook PHENIX has a wide variety of correlation measurements. While each of these measurements targets a specific aspect of angular correlations, when combined reveal a wealth of information about the transverse dynamics at RHIC The correlation methods show asymmetry and anisotropy The asymmetries are consistent with the presence of jets and show striking similarities to pp A scaling relationship for v2 has been established and the differential v2 in AuAu scales with the integral v2. The next step: The scaling might give a good handle to probe jet effects in the data and compare pp to AA Comparisons are currently underway … still many more to come, so stay tuned
Wolf G. Holzmann (SUNY Stony Brook) for the PHENIX Collaboration