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Characterizing the freezeout at RHIC: HBT, spectra, and elliptic flow

Characterizing the freezeout at RHIC: HBT, spectra, and elliptic flow. Mike Lisa, Ohio State University STAR Collaboration. U.S. Labs: Argonne, Lawrence Berkeley National Lab, Brookhaven National Lab U.S. Universities: Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon,

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Characterizing the freezeout at RHIC: HBT, spectra, and elliptic flow

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  1. Characterizing the freezeout at RHIC:HBT, spectra, and elliptic flow Mike Lisa, Ohio State University STAR Collaboration U.S. Labs:Argonne, Lawrence Berkeley National Lab, Brookhaven National Lab U.S. Universities:Arkansas, UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Yale Brazil: Universidade de Sao Paolo China:IHEP - Beijing, IPP - Wuhan England:University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich, University of Frankfurt Poland:Warsaw University, Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR–Dubna, IHEP-Protvino Mike Lisa - ACS Nuclear Division - Chicago

  2. Schematic goal and method - soft physics • Goal: EoS of dense matter - relationship b/t bulk properties (P,T,…) • evidence for phase transition? • Method: • Full characterization of freezeout distribution f(x,p) • Consistent characterization for several observables • Use measurements to constrain EoS via a model (hydro?), which connects early time to freezeout • This talk: • Focus on transverse observables: dN/dpT, v2(pT,m), HBT(pT,f) • Consistent picture within “hydro-inspired” parameterization?(is the data telling a consistent story, and what does it mean?) • identify features of “real” model needing attention Mike Lisa - ACS Nuclear Division - Chicago

  3. An analogous situation… Mike Lisa - ACS Nuclear Division - Chicago

  4. Probing f(x,p) from different angles Transverse spectra: number distribution in mT Elliptic flow: anisotropy as function of mT HBT: homogeneity lengths vs mT, fp Mike Lisa - ACS Nuclear Division - Chicago

  5. mT distribution from Hydrodynamics type model b s R Infinitely long solid cylinder fb = direction of flow boost (= fs here) 2-parameter (T,b) fit to mT distribution E.Schnedermann et al, PRC48 (1993) 2462 Mike Lisa - ACS Nuclear Division - Chicago

  6. Fits to STAR spectra; br=bs(r/R)0.5 K- - - Tth[GeV] K- 1/mT dN/dmT (a.u.) s [c] p p Tth[GeV] Tth[GeV] mT - m[GeV/c2] s [c] s [c] Tth =120+40-30MeV <r >=0.52 ±0.06[c] tanh-1(<r >) = 0.6 • c2 contour maps for 95.5%CL preliminary STAR preliminary <r >= 0.8s thanks to M. Kaneta Mike Lisa - ACS Nuclear Division - Chicago

  7. STAR HBT data for central collisions- further info? conflicting info? p- p+ R(pT) probes interplay b/t space-time geometry and temperature/flow STAR Collab., PRL 87 082301 (2001) Mike Lisa - ACS Nuclear Division - Chicago

  8. Implications for HBT: radii vs pT pT=0.2 y (fm) x (fm) pT=0.4 y (fm) x (fm) Assuming b, T obtained from spectra fits  strong x-p correlations, affecting RO, RS differently Mike Lisa - ACS Nuclear Division - Chicago

  9. Implications for HBT: radii vs pT pT=0.2 y (fm) x (fm) STAR data pT=0.4 y (fm) x (fm) Magnitude of flow and temperature from spectra can account for observed drop in HBT radii via x-p correlations, and Ro<Rs …but emission duration must be small Four parameters affect HBT radii model: R=13.5 fm, t=1.5 fm/c T=0.11 GeV, r0 = 0.6 Mike Lisa - ACS Nuclear Division - Chicago

  10. Joint view of p freezeout: HBT & spectra • common model/parameterset describes different aspects of f(x,p) for central collisions • Increasing T has similar effect on a spectrum as increasing b • But it has opposite effect on R(pT) • opposite parameter correlations in the two analyses tighter constraint on parameters • caviat: not exactly same model used here (different flow profiles) spectra (p) STAR preliminary HBT Mike Lisa - ACS Nuclear Division - Chicago

  11. Non-central collisions:coordinate and momentum-space anisotropies P. Kolb, J. Sollfrank, and U. Heinz Equal energy density lines Mike Lisa - ACS Nuclear Division - Chicago

  12. Elliptic flow (momentum-space anisotropy):sensitive to early pressure / thermalization in-plane enhancement v2 @ SPS: between hydro and LDL P. Kolb, et al., PLB 500 232 (2001) Hydro describes flow quantitatively @ RHIC Mike Lisa - ACS Nuclear Division - Chicago

  13. HBT: (transverse) spatial anisotropy y K side • Source in b-fixed system: (x,y,z) • Space/time entangled in pair system (xO,xS,xL) out f x b large flow @ RHIC induces space-momentum correlations  p-dependent homogeneity lengths  sensitive to more than “just” anisotropic geometry U. Wiedemann, PRC 57, 266 (1998) Mike Lisa - ACS Nuclear Division - Chicago

  14. Reminder: observations for Au(2 AGeV)Au out side long 40 R2 (fm2) 20 os ol sl 10 0 -10 0 0 0 180 180 180 fp (°) interesting physics, but not currenly accessible in STAR with 2nd-order reaction plane E895 Collab., PLB 496 1 (2000) fp=90° fp=0° out-of-plane extended source Lines are global fit Oscillation magnitude  eccentricity Oscillation phases  orientation Mike Lisa - ACS Nuclear Division - Chicago

  15. More detail: identified particle elliptic flow Flow boost: dashed solid T (MeV) 135  20 100  24 0(c) 0.52  0.02 0.54  0.03 a (c) 0.09  0.02 0.04  0.01 S2 0.0 0.04  0.01 hydro-inspired blast-wave model Houvinen et al (2001) fb = boost direction STAR Collab, submitted to PRL Meaning of ra is clear  how to interpret s2? Mike Lisa - ACS Nuclear Division - Chicago

  16. Ambiguity in nature of the spatial anisotroy case 1: circular source with modulating density RMSx > RMSy case 2: elliptical source with uniform density RMSx < RMSy fb = direction of the boost  s2 > 0 means more source elements emitting in plane Mike Lisa - ACS Nuclear Division - Chicago

  17. STAR HBT Correlation function: fp=45º p- from semi-peripheral events 1.3 “Out” C(Q) RO2 (fm2) 1.0 raw corrected for reactionplane resolution 1.3 “Side” RS2 (fm2) 1.0 ROS2 (fm2) 1.3 “Long” 1.0 0 0.1 0.2 Q (GeV/c) STAR preliminary data fit • only mix events with “same” fRP • retain relative sign between q-components • HBT radii oscillations similar to AGS • curves are not a global fit • RS almost flat Mike Lisa - ACS Nuclear Division - Chicago

  18. Out-of-plane elliptical shape indicated using (approximate) values of s2 and ra from elliptical flow case 1 case 2 opposite R(f) oscillations would lead to opposite conclusion STAR preliminary Mike Lisa - ACS Nuclear Division - Chicago

  19. s2 dependence dominates HBT signal s2=0.033, T=100 MeV, r0=0.6 ra=0.033, R=10 fm, t=2 fm/c color: c2 levels from HBT data error contour from elliptic flow data STAR preliminary Mike Lisa - ACS Nuclear Division - Chicago

  20. Time-averaged freezeout shape • close to circular @ RHIC • info on evolution duration? STAR preliminary (E895) Mike Lisa - ACS Nuclear Division - Chicago

  21. Hydro predictions 60 RO2 (fm2) 40 20 15 RS2 (fm2) 10 5 0.8 ROS2 (fm2) 0 -0.8 90 180 0 fp (º) • phases and ~ magnitude of HBT radii oscillations OK • RO too large • RS too small Mike Lisa - ACS Nuclear Division - Chicago

  22. Summary - a consistent picture main source of discrepancy? Mike Lisa - ACS Nuclear Division - Chicago

  23. Summary • Spectra, elliptic flow, and HBT measures consistent with a freeze-out distribution including strong space-momentum correlations • In non-central collisions, v2 measurements sensitive to existence of spatial anisotropy, while HBT measurement reveals its nature • Systematics of HBT parameters: • flow gradients produce pT-dependence (consistent with spectra and v2(pT,m)) • anisotropic geometry (and anisotropic flow boost) produce f-dependence • (average) out-of-plane extension indicated • however, distribution almost “round,” --> more hydro-like evolution as compared to AGS • While data tell consistent story within hydro-inspired parameterization, hydro itself tells a different story - likely point of conflict is timescale Mike Lisa - ACS Nuclear Division - Chicago

  24. Hydro reproduced spectra well Mike Lisa - ACS Nuclear Division - Chicago

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