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Two-particle correlations and Heavy Ion Collision Dynamics at RHIC/STAR

Two-particle correlations and Heavy Ion Collision Dynamics at RHIC/STAR. Mike Lisa, Ohio State University STAR Collaboration. Motivation / STAR Central collision dynamics – spectra & HBT(p T ) Non-central collision dynamics – elliptic flow & HBT( )

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Two-particle correlations and Heavy Ion Collision Dynamics at RHIC/STAR

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  1. Two-particle correlations and Heavy Ion Collision Dynamics at RHIC/STAR Mike Lisa, Ohio State University STAR Collaboration • Motivation / STAR • Central collision dynamics – spectra & HBT(pT) • Non-central collision dynamics – elliptic flow & HBT() • Further info from correlations of non-identical particles • Consistent picture of RHIC dynamics • Conclusions malisa - seminar IUCF

  2. Why heavy ion collisions? The “little bang” • Study bulk properties of nuclear matter • Extreme conditions (high density/temperature) expect a transition to new phase of matter… • Quark-Gluon Plasma (QGP) • partons are relevant degrees of freedom over large length scales (deconfined state) • believed to define universe until ~ ms • Study of QGP crucial to understanding QCD • low-q (nonperturbative) behaviour • confinement (defining property of QCD) • nature of phase transition • Heavy ion collisions ( “little bang”) • the only way to experimentally probe deconfined state malisa - seminar IUCF

  3. Relativistic Heavy Ion Collider (RHIC) PHOBOS BRAHMS 12:00 o’clock BRAHMS PHOBOS RHIC 2:00 o’clock PHENIX 10:00 o’clock STAR RHIC PHENIX 8:00 o’clock 4:00 o’clock STAR 6:00 o’clock AGS 9 GeV/u Q = +79 U-line BAF (NASA) m g-2 LINAC BOOSTER HEP/NP AGS TANDEMS 1 MeV/u Q = +32 TANDEMS • 2 concentric rings of 1740 superconducting magnets • 3.8 km circumference • counter-rotating beams of ions from p to Au • max center-of-mass energy: AuAu 200 GeV, pp 500 GeV RHIC Runs Run I: Au+Au at s = 130 GeV Run II: Au+Au and pp at s = 200 GeV malisa - seminar IUCF

  4. The STAR Collaboration • 451 Collaborators (294 authors) • 45 Institutions • 9 Countries: • Brazil, China, England, France, Germany, India, Poland, Russia, US malisa - seminar IUCF

  5. Geometry of STAR Magnet Time Projection Chamber Coils SiliconVertexTracker TPC Endcap & MWPC FTPCs ZCal ZCal VertexPositionDetectors Endcap Calorimeter Central Trigger Barrel or TOF BarrelEMCalorimeter RICH malisa - seminar IUCF

  6. Au on Au Event at CM Energy ~ 130 AGeV Event Taken June 25, 2000. malisa - seminar IUCF

  7. Particle ID in STAR RICH dE/dx dE/dx PID range: [s (dE/dx) = .08] p  ~ 0.7 GeV/c for K/  ~ 1.0 GeV/c for p/p RICH PID range: 1 - 3 GeV/c for K/ 1.5 - 5 GeV/c for p/p f from K+ K- pairs dn/dm background subtracted Topology Decay vertices Ks p + + p - L  p + p - L  p + p + X - L + p - X +L + p + W  L + K - Combinatorics Ks p + + p - f  K + + K - L  p + p - L  p + p + [ r  p + + p -] [D  p + p -] m inv kaons protons dn/dm deuterons K+ K- pairs pions same event dist. mixed event dist. Vo m inv electrons STAR “kinks”: K  +  malisa - seminar IUCF

  8. Kaon Spectra at Mid-rapidity vs Centrality K- K+ (K++K-)/2 Ks Centrality cuts Centrality cuts Centrality cuts 0-6% 0-6% 0-6% 11-18% 11-18% 11-18% 26-34% 26-34% 26-34% 45-58% 45-58% 45-58% 58-85% 58-85% 58-85% STAR preliminary STAR preliminary STAR preliminary Exponential fits to mT spectra: Good agreement between different PID methods malisa - seminar IUCF

  9. Hadrochemistry: particle yields vs statistical models malisa - seminar IUCF

  10. lattice QCD applies malisa - seminar IUCF

  11. Already producing QGP at lower energy? • Thermal model fits to particle yields(including strangeness, J/) •  approach QGP at CERN? • is the system really thermal? • warning: e+e- falls on similar line!! • dynamical signatures? (no) • what was pressure generated? • what is Equation of State of strongly-interacting matter? • Must go beyond chemistry: • study dynamics of system well into • deconfined phase (RHIC) lattice QCD applies malisa - seminar IUCF

  12. Collision dynamics - several timescales dN/dt “temperature” 1 fm/c ? 5 fm/c ? 10 fm/c ? 50 fm/c ? time low-pT hadronic observables hadronic phase and freeze-out QGP and hydrodynamic expansion hadronization initial state pre-equilibrium Chemical freeze out “end result” looks very similar whether a QGP was formed or not!!! Kinetic freeze out malisa - seminar IUCF

  13. First RHIC spectra - an explosive source purely thermal source light 1/mT dN/dmT heavy mT explosive source light T,b T 1/mT dN/dmT heavy mT • various experiments agree well • different spectral shapes for particles of differing mass strong collective radial flow • very good agreement with hydrodynamicprediction data: STAR, PHENIX, QM01 model: P. Kolb, U. Heinz malisa - seminar IUCF

  14. Hydrodynamics: modeling high-density scenarios • Assumes local thermal equilibrium (zero mean-free-path limit) and solves equations of motion for fluid elements (not particles) • Equations given by continuity, conservation laws, and Equation of State (EOS) • EOS relates quantities like pressure, temperature, chemical potential, volume • direct access to underlying physics • Works qualitatively at lower energybut always overpredicts collectiveeffects - infinite scattering limitnot valid there • RHIC is first time hydro works! lattice QCD input malisa - seminar IUCF

  15. “Blast wave” Thermal motion superimposed on radial flow (+ geometry) b s s R Hydro-inspired “blast-wave” thermal freeze-out fits to p, K, p, L preliminary Tth = 107 MeV b = 0.55 M. Kaneta E.Schnedermann et al, PRC48 (1993) 2462 malisa - seminar IUCF

  16. The other half of the story… • Momentum-space characteristics of freeze-out appear well understood • Coordinate-space ? • Probe with two-particle intensity interferometry (“HBT”) malisa - seminar IUCF

  17. “HBT 101” - probing source geometry 1-particle probability r(x,p) = U*U 2-particle probability F.T. of pion source Measurable! p1 r1 x1 p source r(x) 1 m x2 r2 p2 5 fm malisa - seminar IUCF

  18. “HBT 101” - probing the timescale of emission K Rout Rside beware this “helpful” mnemonic! Decompose q into components: qLong: in beam direction qOut : in direction of transverse momentum qSide:  qLong & qOut (beam is into board) malisa - seminar IUCF

  19. Large lifetime - a favorite signal of “new” physics at RHIC 3D 1-fluid Hydrodynamics with transition Rischke & Gyulassy NPA 608, 479 (1996) ec “e” • hadronization time (burning log) will increase emission timescale (“lifetime”) • magnitude of predicted effect depends strongly on nature of transition • measurements at lower energies (SPS, AGS) observe t<~3 fm/c t ~ …but lifetime determination is complicated by other factors… malisa - seminar IUCF

  20. First HBT data at RHIC “raw” correlation function projection Coulomb-corrected (5 fm full Coulomb-wave) Data well-fit by Gaussian parametrization 1D projections of 3D correlation function integrated over 35 MeV/cin unplotted components STAR Collab., PRL 87 082301 (2001) malisa - seminar IUCF

  21. HBT excitation function midrapidity, low pTp- from central AuAu/PbPb • decreasing l parameter partially due to resonances • saturation in radii • geometric or dynamic (thermal/flow) saturation • the “action” is ~ 10 GeV (!) • no jump in effective lifetime • NO predicted Ro/Rs increase(theorists: data must be wrong) • Lower energy running needed!? STAR Collab., PRL 87 082301 (2001) malisa - seminar IUCF

  22. Central collision dynamics @ RHIC • Hydrodynamics reproduces p-space aspects of particle emission up to pT~2GeV/c (99% of particles) hopes of exploring the early, dense stage malisa - seminar IUCF Heinz & Kolb, hep-th/0204061

  23. Central collision dynamics @ RHIC • Hydrodynamics reproduces p-space aspects of particle emission up to pT~2GeV/c (99% of particles) hopes of exploring the early, dense stage • x-space is poorly reproduced • model source is too small and lives too long and disintegrates too slowly? • Correct dynamics signatures with wrong space-time dynamics? • The RHIC HBT Puzzle • Is there any consistent way to understand the data? • Try to understand in simplest way possible malisa - seminar IUCF Heinz & Kolb, hep-th/0204061

  24. Blastwave parameterization:Implications for HBT: radii vs pT K K Assuming b, T obtained from spectra fits  strong x-p correlations, affecting RO, RS differently pT=0.2 RO RS pT=0.4 “whole source” not viewed malisa - seminar IUCF

  25. Blastwave: radii vs pT K K pT=0.2 STAR data Using 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 blastwave: R=13.5 fm, tfreezeout=1.5 fm/c pT=0.4 malisa - seminar IUCF

  26. Simple Sinyukov formula RL2 = tkinetic2 T/mT tkinetic = 10 fm/c (T=110 MeV) B. Tomasik (~3D blast wave) tkinetic = 8-9 fm/c From Rlong:tkinetic = 8-10 fm/c (fast!) malisa - seminar IUCF

  27. Noncentral collision dynamics or hydro evolution • Dynamical models: • x-anisotropy in entrance channel  p-space anisotropy at freezeout • magnitude depends on system response to pressure malisa - seminar IUCF

  28. Noncentral collision dynamics • hydro reproduces v2(pT,m) (details!) @ RHIC for pT < ~1.5 GeV/c • system response  EoS • early thermalization indicated Heinz & Kolb, hep-ph/0111075 hydro evolution • Dynamical models: • x-anisotropy in entrance channel  p-space anisotropy at freezeout • magnitude depends on system response to pressure malisa - seminar IUCF

  29. Effect of dilute stage later hadronic stage? hydro evolution • hydro reproduces v2(pT,m) (details!) @ RHIC for pT < ~1.0 GeV/c • system response  EoS • early thermalization indicated RHIC • dilute hadronic stage (RQMD): • little effect on v2 @ RHIC SPS malisa - seminar IUCF Teaney, Lauret, & Shuryak, nucl-th/0110037

  30. Effect of dilute stage later hadronic stage? hydro only hydro+hadronic rescatt STAR PHENIX hydro evolution • hydro reproduces v2(pT,m) (details!) @ RHIC for pT < ~1.5 GeV/c • system response  EoS • early thermalization indicated • dilute hadronic stage (RQMD): • little effect on v2 @ RHIC • significant (bad) effect on HBT radii calculation: Soff, Bass, Dumitru, PRL 2001 malisa - seminar IUCF

  31. Effect of dilute stage later hadronic stage? hydro evolution • hydro reproduces v2(pT,m) (details!) @ RHIC for pT < ~1.5 GeV/c • system response  EoS • early thermalization indicated • dilute hadronic stage (RQMD): • little effect on v2 @ RHIC • significant (bad) effect on HBT radii • related to timescale? - need more info malisa - seminar IUCF Teaney, Lauret, & Shuryak, nucl-th/0110037

  32. Effect of dilute stage later hadronic stage? in-plane-extended out-of-plane-extended hydro evolution • hydro reproduces v2(pT,m) (details!) @ RHIC for pT < ~1.5 GeV/c • system response  EoS • early thermalization indicated • dilute hadronic stage (RQMD): • little effect on v2 @ RHIC • significant (bad) effect on HBT radii • related to timescale? - need more info • qualitative change of freezeout shape!! • important piece of the puzzle! malisa - seminar IUCF Teaney, Lauret, & Shuryak, nucl-th/0110037

  33. Possible to “see” via HBT relative to reaction plane? fp=90° Rside (small) Rside (large) fp=0° • for out-of-plane-extended source, expect • large Rside at 0 • small Rside at 90 2nd-order oscillation Rs2 [no flow expectation] fp malisa - seminar IUCF

  34. “Traditional HBT” - cylindrical sources(reminder) K Rout Rside Decompose q into components: qLong: in beam direction qOut : in direction of transverse momentum qSide:  qLong & qOut (beam is into board) malisa - seminar IUCF

  35. Anisotropic sources Six HBT radii vs f side y K out • Source in b-fixed system: (x,y,z) • Space/time entangled in pair system (xO,xS,xL) fp x b ! • explicit and implicit (xmxn(f)) dependence on f malisa - seminar IUCF Wiedemann, PRC57 266 (1998).

  36. Symmetries of the emission function I. Mirror reflection symmetry w.r.t. reactionplane (for spherical nuclei):  with II. Point reflection symmetry w.r.t. collision center (equal nuclei):  with Heinz, Hummel, MAL, Wiedemann, nucl-th/0207003 malisa - seminar IUCF

  37. Fourier expansion of HBT radii @ Y=0 Insert symmetry constraints of spatial correlation tensor into Wiedemann relations and combine with explicit F-dependence: Note: These most general forms of the Fourier expansions for the HBT radii are preserved when averaging the correlation function over a finite, symmetric window around Y=0. Relations between the Fourier coefficients reveal interplay between flow and geometry, and can help disentangle space and time malisa - seminar IUCF Heinz, Hummel, MAL, Wiedemann, nucl-th/0207003

  38. Anisotropic HBT results @ AGS (s~2 AGeV) out side long 40 R2 (fm2) 20 os ol sl 10 0 -10 0 0 0 180 180 180 fp (°) Au+Au 2 AGeV; E895, PLB 496 1 (2000) xside xout K fp = 0° • strong oscillations observed • lines: predictions for static (tilted) out-of-plane extended source  consistent with initial overlap geometry malisa - seminar IUCF

  39. Meaning of Ro2(f) and Rs2(f) are clearWhat about Ros2(f) ? out side long xside 40 R2 (fm2) xside xside xside xside xside xside xout xout xout xout xout xout xout 20 K os ol sl 10 K K K K K K 0 -10 0 0 0 180 180 180 No access to 1st-order oscillations in STAR Y1 fp (°) Au+Au 2 AGeV; E895, PLB 496 1 (2000) fp = 0° fp ~45° • Ros2(f) quantifies correlation between xout and xside • No correlation (tilt) b/t between xout and xside at fp=0° (or 90°) • Strong (positive) correlation when fp=45° • Phase of Ros2(f) oscillation reveals orientation of extended source malisa - seminar IUCF

  40. Indirect indications of x-space anisotropy @ RHIC 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 • v2(pT,m) globally well-fit by hydro-inspired “blast-wave”(Houvinen et al) temperature, radial flow consistent with fits to spectra  anisotropy of flow boost spatial anisotropy (out-of-plane extended) malisa - seminar IUCF STAR, PRL 87 182301 (2001)

  41. STAR data Au+Au 130 GeV minbias full blastwave consistent with R(pT), K-p • significant oscillations observed • blastwave with ~ same parameters as used to describe spectra & v2(pT,m) • additional parameters: • R = 11 fm •  = 2 fm/c !! preliminary malisa - seminar IUCF

  42. STAR data Au+Au 130 GeV minbias full blastwave no flow anisotropy consistent with R(pT), K-p no spatial anisotropy • significant oscillations observed • blastwave with ~ same parameters as used to describe spectra & v2(pT,m) • additional parameters: • R = 11 fm •  = 2 fm/c !! preliminary • both flow anisotropy and source shape contribute to oscillations, but… • geometry dominates dynamics • freezeout source out-of-plane extended fast freeze-out timescale ! (7-9 fm/c) malisa - seminar IUCF

  43. Azimuthal HBT: hydro predictions • RHIC (T0=340 MeV @ t0=0.6 fm) • Out-of-plane-extended source (but flips with hadronic afterburner) • flow & geometry work together to produce HBT oscillations • oscillations stable with KT (note: RO/RS puzzle persists) Heinz & Kolb, hep-th/0204061 malisa - seminar IUCF

  44. Azimuthal HBT: hydro predictions • RHIC (T0=340 MeV @ t0=0.6 fm) • Out-of-plane-extended source (but flips with hadronic afterburner) • flow & geometry work together to produce HBT oscillations • oscillations stable with KT • “LHC” (T0=2.0 GeV @ t0=0.1 fm) • In-plane-extended source (!) • HBT oscillations reflect competition between geometry, flow • low KT: geometry • high KT: flow sign flip Heinz & Kolb, hep-th/0204061 malisa - seminar IUCF

  45. HBT(φ) Results – 200 GeV STAR PRELIMINARY • Oscillations similar to those measured @ 130GeV • 20x more statistics explore systematics in centrality, kT • much more to come… malisa - seminar IUCF

  46. Smaller source  stronger (anti)correlation K-p correlation well-described by: Blast wave with same parameters as spectra, HBT But with non-identical particles, we can access more information… Kaon – pion correlations:dominated by Coulomb interaction STAR preliminary Adam Kiesel, Fabrice Retiere malisa - seminar IUCF

  47. Initial idea: probing emission-time ordering • Catching up: cosY  0 • long interaction time • strong correlation • Moving away: cosY  0 • short interaction time • weak correlation • Ratio of both scenarios allow quantitative study of the emission asymmetry purple K emitted first green p is faster purple K emitted first green p is slower Crucial point: kaon begins farther in “out” direction (in this case due to time-ordering) malisa - seminar IUCF

  48. clear space-time asymmetry observed C+/C- ratio described by: “standard” blastwave w/ no time shift Direct proof of radial flow-induced space-momentum correlations measured K-p correlations - natural consequence of space-momentum correlations STAR preliminary Pion <pt> = 0.12 GeV/c Kaon <pt> = 0.42 GeV/c malisa - seminar IUCF

  49. Summary RHIC 130 GeV Au+Au K* K- Tomasik (3D blastwave): 8-9 fm/c (fit to PHENIX even smaller) Sinyukov formula: Rlong2=t2T/mT = 10 fm/c for T=110 MeV Disclaimer: all numbers (especially time) are rough estimates malisa - seminar IUCF

  50. Summary RHI – the only way to create/study deconfined colored matter Hadrochemistry suggests creation of QGP @ RHIC (and SPS) Quantitative understanding of bulkdynamics crucial to extracting real physics at RHIC • p-space - measurements well-reproduced by models • anisotropy [v2(pT,m)]  system response to compression (EoS) • x-space - generally not well-reproduced • anisotropy [HBT()] evolution, timescale information, geometry/flow interplay • Azimuthally-sensitive HBT: correlating quantum correlation with bulk correlation • reconstruction of full 3D source geometry • relevant here: OOP freeze-out • Data do suggest consistent (though surprising) scenario • strong collective effects • rapid evolution, then emission in a “flash” (key input to models) • where is the hadronic phase? • K-, HBT(pT), HBT(), K*… By combining several (novel) measurements, STAR severely challenges our understanding of dynamics in the soft sector of RHIC malisa - seminar IUCF

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