Lanny RayOhio State Seminar - July 29, Large Scale Correlations and the Dissipative Medium Produced in Au+Au Collisions at RHIC Lanny Ray University of Texas at Austin Ohio State University, July 29, 2003

Lanny RayOhio State Seminar - July 29, Acknowledgements: STAR Collaboration Event Structure Working Group With special thanks to my collaborators whose work will be shown: Aya Ishihara - thesis work included (U. Texas Ph.D. student) Jeff Reid - thesis work included (U. Washington, Post Doc) Qingjun Liu - (U. Washington, Post Doc) Zubayer Ahammed - (Purdue U. Post Doc) Tom Trainor - (U. Washington)

Lanny RayOhio State Seminar - July 29, RHIC at BNL STAR

Lanny RayOhio State Seminar - July 29, E-M Calorimeter Time of Flight Projection Chamber The STAR detector

Lanny RayOhio State Seminar - July 29, hadronization initial statepre-equilibrium STAR Event viewed along beam axis decoupling ? Graphics from Steffen Bass and John Harris x z y I. The general view of RHIC collisions typical minimum bias event

Lanny RayOhio State Seminar - July 29, Color string fragmentation, charge ordering, local momentum conservation, bulk production at midrapidity from hot, dense medium Also hard and semi-hard pQCD processes which punch into medium How does the hot, dense medium respond? What’s happening just after the nuclei collide?

Lanny RayOhio State Seminar - July 29, STAR’s large acceptance Short-range dynamics; non-statistical fluctuations Large momentum scale correlations Initial state scattering (soft & pQCD), color string fragmentation along beam axis and transverse toward detector Processes modified by developing, dissipative medium Medium fluctuates as a result of semi-hard punches We’ll measure the response of medium to learn about its properties What’s our game plan?

Lanny RayOhio State Seminar - July 29, II. Mean Transverse Momentum Fluctuation Analysis GeV Event cuts:  event vertex |z| < 75cm, |x|,|y| < 1cm Track cuts:  0.1 < p t < 2 GeV   |<1.0, full 2  Principal Authors: Ahammed, LR, Reid (thesis), Trainor 183k central trigger events (15%) 205k minimum bias events x z y

Lanny RayOhio State Seminar - July 29, Inclusive p t distribution, (all particles in all events) Randomly sample this distribution n times to make “events” with multiplicity n. Compute the event-wise for these “events.” Reduced width given by: Central Limit Theorem results Statistical reference with which to compare real events

Lanny RayOhio State Seminar - July 29, K top 15% central events using 70% of all primary particles Both (+) and (-) charges |  | < 1, full  0.1 < p t < 2.0 GeV/c Nonstatistical fluctuations increase the rms width by (syst)% Centered at 0 In units of expected rms from CLT Gamma dist. with increased rms Statistical ref. from inclusive p T spectrum* STAR Preliminary (*) N sampled inclusive spectrum approx. equals Gamma dist. Event-wise distribution:

Lanny RayOhio State Seminar - July 29, (See: Quantitative Mean p t Fluctuation Analysis (removes multiplicity fluctuation bias) (Direct application of CLT) (Analogous to dx 2 =2xdx) This last step defines a fluctuation measure linear in the mean p t distribution width Relation to  pt of Gazdzicki and Mrowczynski, Z. Phys. C 54, 127 (1992). (variance increase)

Lanny RayOhio State Seminar - July 29, Numerical measures of mean-p t fluctuations CI CD x 3 205K minbias events 70% of primaries Extrapolated to 100% +0.5 MeV/c stat. errors +20% syst. Errors DCA cut < 3 cm  Strong nonstatistical fluctuations  Centrality dependence  CI larger than at SPS (more later)  CD smaller at RHIC  PHENIX null result is not inconsistent with STAR’s measurement (more later) STAR Preliminary Charge-independent: CI = [(++)+(--)]+[(+-)+(-+)] Charge-dependent: CD = [(++)+(--)]-[(+-)+(-+)] centrality Extrapolation to 100% 70% of primaries

Lanny RayOhio State Seminar - July 29, estimates average path length Glauber-model : mean path length Stochastic multiple scattering scales as  (path length) Saturation - dissipation for most central events? STAR Preliminary Binary collisions, Path length and

Lanny RayOhio State Seminar - July 29, Status of comparisons with SPS, PHENIX and Hijing CERES experiment at CERN-SPS (Adamova et al., nucl-ex/ ) measured  pt = 3.3 +/- 2 MeV/c for Pb+Au at lab energy of 158 AGeV (fixed target), [17 GeV/NN (cm)] for N = 162 and  PHENIX at RHIC [Adcox et al., PR C66, (2002)] measured  pt = 6+/-6 MeV/c for Au+Au at 130 GeV/c for  0.35 and |  | = 58.5 deg. for top 5% central events. STAR (almost submitted to PRL) measured  pt =14+/-2 MeV/c for N = 180 and |  |<0.25 which is 4-5 times larger. STAR also measured  pt =9+/-1 MeV/c at the PHENIX acceptance. NA49 [Appelshausser et al., Phys. Lett. B459, 679 (1999)] measured  pt =0.6+/-1 MeV/c for Pb+Pb at 158 AGeV for N = 270 and y cm =[1.1,2.6].

II. p t  p t Charge Average (CI) Correlations 130 GeV PAs: Ishihara (thesis), Trainor, LR

Lanny RayOhio State Seminar - July 29, Two-Particle Correlations and Kinematics Useful kinematics: Projection onto 2D subspaces: z, beam x y  Relation of variance to correlations Differential study of nonstatistical fluctuations

Lanny RayOhio State Seminar - July 29, Projected, Two-Point Correlations Count # pairs in (  ) 2D bin from same events (“siblings”) Count # pairs in (  ) 2D bin from different events (“mixed”) The 2D bin counts are easily obtained as the product of (# in bin-  x (# in bin-  Number Density  p t Event p t1 p t2 Numerator Denominator   We can do this for any measure, e.g. p t,, E, net Q,... bins

Lanny RayOhio State Seminar - July 29, Construct the Correlation Sum numerator and denominator over all events in ensemble, g divide, and normalize using total number of sibling and mixed event pairs. Differences from 1.0 indicate correlations. g (Ratios formed using similar events, then r’s summed over all events.) Correlations example only, not actual data

Lanny RayOhio State Seminar - July 29, p t x p t two-point number density ratios for Au+Au at 130 GeV Central 21% by multiplicity ~100k events 0.15 < p t <2 GeV/c |  |<1.3, full  (produces flat dist. on X) (1) HBT+Coul. at low p t. (2) Stochastic semi-hard scattering and fragmentation at larger p t (3) Overall “saddle” shape due to fluctuations in bulk medium; measured by curvature [Sum-diag (main) up - Diff-diag (off) down]. STAR Preliminary Like signUnlike sign

Lanny RayOhio State Seminar - July 29, p t x p t two-point number density ratios for Au+Au at 130 GeV most- central peripheral r[X(p t1 ),X(p t2 )]-1 for all charges STAR Preliminary HBT,Coul. removed using track pair cuts

Lanny RayOhio State Seminar - July 29, Fitting the p t x p t two-point number density ratios for Au+Au at 130 GeV - remove HBT, Coul. - exclude higher p t peak from fit - use analytical 2D “saddle” shape derived from fluctuating two-point temperature model modelresidual Project residuals onto sum direction, X  =X(p t1 )+X(p t2 ), and integrate peak STAR Preliminary

Lanny RayOhio State Seminar - July 29, p t x p t two-point number density ratios for Au+Au at 130 GeV - Summary Plot curvature vs path length  (concave up along X  - concave down along X  )x(N) Plot integral (xN) of high pt residual vs  IWe observe semi-hard scattering production which increases with initial state path length. IWe also observe increasing fluctuations in the bulk medium. IA possible interpretation is that with increasing centrality dissipation of p t from initial state semi-hard scattering processes into the soft p t bulk medium is increased. STAR Preliminary

III.      CD Correlations GeV PAs: Ishihara (thesis), Trainor, LR             

Lanny RayOhio State Seminar - July 29, Forming the CD Joint Autocorrelation CD = LS  US CI = LS + US CI - initial-state scattering CD - final-state hadronization LSUS individual two-point spacesjoint autocorrelations STAR Preliminary charge ordering elliptic flow, plus...

Lanny RayOhio State Seminar - July 29,   x   CD Data 1D autocorrelation projections with fits 2D joint autocorrelations   these are two-point number densities STAR Preliminary

Lanny RayOhio State Seminar - July 29,   x   CD Summary Short-range correlations (SRC) well-studied in elementary collisions, this work extends such studies to A-A collisions Possible interpretation is that these data are consistent with correlated pairs escaping from an opaque medium - reduced mean free path - escape probability falls exponentially with opening angle Alternative hypothesis: e.g. distortion of opening-angle distribution by large radial flow Study changing geometry of hadronization - from 1D string fragmentation  2+D surface emission in A-A, which is an open issue in QCD phenomenology

IV.  -  Scaling of Fluctuations PAs: Liu, Trainor

Lanny RayOhio State Seminar - July 29, What is a scaled correlation analysis? The idea is to measure fluctuations on one kinematic variable (e.g. p t ) while binning on orthogonal directions (e.g.  ): acceptancebin size or scale avg. over events sum occupied. bins function of scale compute variance among pairs in all (  bins in the acceptance The scale dependence reveals correlations: Invert Volterra eq. in its discrete form, obtain autocorrelation

Lanny RayOhio State Seminar - July 29, Transverse momentum scaling analysis for Au+Au at 200 GeV  pt (CI) as function of scale   p t auto- correlation on axial space   peripheral midcentral most-central -Same side correlation -Away side p conserv. -Elliptical flow, plus ? -Away side suppression with centrality -Dissipation of away side p t into bulk STAR Preliminary

Lanny RayOhio State Seminar - July 29, Conclusions Large, non-statistical CI fluctuations; centrality dependence at RHIC. Structure in p t  p t CI and      CD distributions seen; data fit with simple, analytic functions. CD      correlations possibly suggest growth of an opaque medium p t  p t CI correlations possibly suggest a dissipative system, with space-correlated temperature fluctuations, and a non-dissipated hard component increasing with centrality. Close connection between correlations and variance scale differences. This evidence suggests that semi-hard ISS processes excite a dissipative and opaque medium, generating the observed CI, CD correlation structure.

Lanny RayOhio State Seminar - July 29, Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino U.S. Laboratories: Argonne Berkeley Brookhaven U.S. Universities: UC Berkeley UC Davis UC Los Angeles Carnegie Mellon Creighton University Indiana University Kent State University Michigan State University City College of New York Ohio State University Penn. State University Purdue University Rice University Texas A&M UT Austin U. of Washington Wayne State University Yale University Brazil: Universidade de Sao Paulo China: IHEP – Beijing IMP - Lanzou IPP – Wuhan USTC SINR – Shanghai Tsinghua University Great Britain: University of Birmingham France: IReS Strasbourg SUBATECH - Nantes Germany: MPI – Munich University of Frankfurt India: IOP - Bhubaneswar VECC - Calcutta Panjab University University of Rajasthan Jammu University IIT - Bombay VECC – Kolcata Poland: Warsaw University of Tech. The STAR Collaboration

Lanny RayOhio State Seminar - July 29,