Large Scale Correlations and the Dissipative Medium Produced in Au+Au Collisions at RHIC

1. 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 Ohio State Seminar - July 29, 2003

2. 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) Ohio State Seminar - July 29, 2003

3. RHIC at BNL STAR Ohio State Seminar - July 29, 2003

4. The STAR detector E-M Calorimeter Projection           Chamber Time of    Flight Ohio State Seminar - July 29, 2003

5. z y x I. The general view of RHIC collisions ? initial state pre-equilibrium hadronization decoupling typical minimum bias event STAR Event viewed along beam axis Graphics from Steffen Bass and John Harris Ohio State Seminar - July 29, 2003

6. - + What’s happening just after the nuclei collide? 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? Ohio State Seminar - July 29, 2003

7. What’s our game plan? STAR’s large acceptance Large momentum scale correlations Short-range dynamics; non-statistical fluctuations 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 Ohio State Seminar - July 29, 2003

8. z y x II. Mean Transverse Momentum Fluctuation Analysis - Au+Au @ 130 GeV Principal Authors: Ahammed, LR, Reid (thesis), Trainor 183k central trigger events (15%) 205k minimum bias events • Event cuts: • event vertex |z| < 75cm, |x|,|y| < 1cm Track cuts: • 0.1 < pt < 2 GeV • |h|<1.0, full 2p Ohio State Seminar - July 29, 2003

9. Statistical reference with which to compare real events Inclusive pt distribution, (all particles in all events) Randomly sample this distribution n times to make “events” with multiplicity n. Compute the event-wise <pt> for these “events.” Reduced width given by: Central Limit Theorem results Ohio State Seminar - July 29, 2003

10. Event-wise <pt> distribution: Nonstatistical fluctuations increase the rms width by 13.7+1.3(syst)% Gamma dist. with increased rms Statistical ref. from inclusive pT spectrum* 183K top 15% central events using 70% of all primary particles Both (+) and (-) charges |h| < 1, full f 0.1 < pt < 2.0 GeV/c STAR Preliminary (*) N sampled inclusive spectrum approx. equals Gamma dist. In units of expected rms from CLT Centered at 0 Ohio State Seminar - July 29, 2003

11. Quantitative Mean pt Fluctuation Analysis (See: www.rhip.utexas.edu/projects/Star/ebye/meanpt) (variance increase) (removes multiplicity fluctuation bias) (Direct application of CLT) (Analogous to dx2=2xdx) This last step defines a fluctuation measure linear in the mean pt distribution width Relation to Fpt of Gazdzicki and Mrowczynski, Z. Phys. C 54, 127 (1992). Ohio State Seminar - July 29, 2003

12. Numerical measures of mean-pt fluctuations Charge-independent: CI = [(++)+(--)]+[(+-)+(-+)] Charge-dependent: CD = [(++)+(--)]-[(+-)+(-+)] Extrapolation to 100% CI 70% of primaries STAR Preliminary 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 centrality • 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) Ohio State Seminar - July 29, 2003

13. Binary collisions, Path length and n n estimates average path length <l> STAR Preliminary • Glauber-model n: mean path length < l> • Stochastic multiple scattering scales as n (path length) Saturation - dissipation for most central events? Ohio State Seminar - July 29, 2003

14. Status of <pt> comparisons with SPS, PHENIX and Hijing CERES experiment at CERN-SPS (Adamova et al., nucl-ex/0305002) measured Fpt = 3.3 +/- 2 MeV/c for Pb+Au at lab energy of 158 AGeV (fixed target), [17 GeV/NN (cm)] for N = 162 and |h|<0.25. STAR (almost submitted to PRL) measured Dspt=14+/-2 MeV/c for N = 180 and |h|<0.25 which is 4-5 times larger. PHENIX at RHIC [Adcox et al., PR C66, 024901 (2002)] measured Fpt = 6+/-6 MeV/c for Au+Au at 130 GeV/c for |h|<0.35 and |Df| = 58.5 deg. for top 5% central events. STAR also measured Dspt=9+/-1 MeV/c at the PHENIX acceptance. NA49 [Appelshausser et al., Phys. Lett. B459, 679 (1999)] measured Fpt=0.6+/-1 MeV/c for Pb+Pb at 158 AGeV for N = 270 and ycm=[1.1,2.6]. Ohio State Seminar - July 29, 2003

15. II. ptpt Charge Average (CI) CorrelationsAu+Au @ 130 GeV PAs: Ishihara (thesis), Trainor, LR

16. Two-Particle Correlations and Kinematics y f x Useful kinematics: z, beam Projection onto 2D subspaces: Relation of variance to correlations Differential study of nonstatistical fluctuations Ohio State Seminar - July 29, 2003

17. Projected, Two-Point Correlations Event 1 2 3 4 5 bins a b pt a b pt Count # pairs in (a,b) 2D bin from same events (“siblings”) Count # pairs in (a,b) 2D bin from different events (“mixed”) pt2 pt2 b b Numerator Denominator The 2D bin counts are easily obtained as the product of (# in bin-a) x (# in bin-b) Number Density pt1 pt1 a a We can do this for any measure, e.g. pt, <pt>, E, net Q, ... Ohio State Seminar - July 29, 2003

18. 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.) 1.01 1.00 example only, not actual data 0.99 Correlations Ohio State Seminar - July 29, 2003

19. pt x pt two-point number density ratios for Au+Au at 130 GeV Like sign Unlike sign Central 21% by multiplicity ~100k events 0.15 < pt<2 GeV/c |h|<1.3, full f=2p STAR Preliminary (1) HBT+Coul. at low pt. (2) Stochastic semi-hard scattering and fragmentation at larger pt (3) Overall “saddle” shape due to fluctuations in bulk medium; measured by curvature [Sum-diag (main) up - Diff-diag (off) down]. (produces flat dist. on X) Ohio State Seminar - July 29, 2003

20. pt x pt two-point number density ratios for Au+Au at 130 GeV r[X(pt1),X(pt2)]-1 for all charges most- central HBT,Coul. removed using track pair cuts STAR Preliminary peripheral Ohio State Seminar - July 29, 2003

21. Fitting the pt x pt two-point number density ratios for Au+Au at 130 GeV STAR Preliminary - remove HBT, Coul. - exclude higher pt peak from fit - use analytical 2D “saddle” shape derived from fluctuating two-point temperature model Project residuals onto sum direction, XS=X(pt1)+X(pt2), and integrate peak model residual Ohio State Seminar - July 29, 2003

22. pt x pt two-point number density ratios for Au+Au at 130 GeV - Summary Plot curvature vs path length n: (concave up along XS - concave down along XD)x(N) Plot integral (xN) of high pt residual vs n: STAR Preliminary n • We observe semi-hard scattering production which • increases with initial state path length. • We also observe increasing fluctuations in the bulk medium. • A possible interpretation is that with increasing centrality • dissipation of pt from initial state semi-hard scattering • processes into the soft pt bulk medium is increased. Ohio State Seminar - July 29, 2003

23. III. hD fD CD Correlations Au+Au @130 GeV PAs: Ishihara (thesis), Trainor, LR hD = (h1 - h2) fD = (f1 - f2)

24. CD = LS - US CI = LS + US CI - initial-state scattering CD - final-state hadronization Forming the CD Joint Autocorrelation individual two-point spaces joint autocorrelations LS US STAR Preliminary charge ordering STAR Preliminary elliptic flow, plus... Ohio State Seminar - July 29, 2003

25. hDxfDCD Data these are two-point number densities 2D joint autocorrelations STAR Preliminary 1D autocorrelation projections with fits STAR Preliminary hD fD Ohio State Seminar - July 29, 2003

26. 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 hDxfDCD Summary Ohio State Seminar - July 29, 2003

27. IV. h-f Scaling of Fluctuations PAs: Liu, Trainor

28. What is a scaled correlation analysis? The idea is to measure fluctuations on one kinematic variable (e.g. pt) while binning on orthogonal directions (e.g.h,f): function of scale acceptance bin size or scale avg. over events sum occupied. bins compute variance among pairs in all (dh,df) bins in the acceptance The scale dependence reveals correlations: Invert Volterra eq. in its discrete form, obtain autocorrelation Ohio State Seminar - July 29, 2003

29. Transverse momentum scaling analysis for Au+Au at 200 GeV Dspt(CI) as function of scale pt auto- correlation on axial space peripheral -Same side correlation -Away side p conserv. -Elliptical flow, plus ? -Away side suppression with centrality -Dissipation of away side ptinto bulk midcentral STAR Preliminary most-central df fD hD dh Ohio State Seminar - July 29, 2003

30. Large, non-statistical <pt> CI fluctuations; centrality dependence at RHIC. Structure in ptpt CI and hDfD CD distributions seen; data fit with simple, analytic functions. CD hDfD correlations possibly suggest growth of an opaque medium ptpt 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. Conclusions This evidence suggests that semi-hard ISS processes excite a dissipative and opaque medium, generating the observed CI, CD correlation structure. Ohio State Seminar - July 29, 2003

31. The STAR Collaboration 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. 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 Ohio State Seminar - July 29, 2003

32. Ohio State Seminar - July 29, 2003