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Dynamic timescales from STAR Year1

Dynamic timescales from STAR Year1. Mike Lisa, Ohio State University , STAR Collaboration. Overview. ~ 1.5 year from initial data-taking in new energy regime ( s=130 GeV) overall picture / underlying driving physics not fully clear Outline Ultrarelativistic heavy ion collisions

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Dynamic timescales from STAR Year1

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  1. Dynamic timescales from STAR Year1 Mike Lisa, Ohio State University, STAR Collaboration malisa - colloquium at Duke

  2. Overview • ~ 1.5 year from initial data-taking in new energy regime (s=130 GeV) • overall picture / underlying driving physics not fully clear • Outline • Ultrarelativistic heavy ion collisions • STAR at RHIC • Collective (radial and elliptic) flow measurements • Initial quantitative success of hydrodynamics • Blast-wave parameterization • Two-particle correlations (HBT) • STAR HBT and the “HBT Puzzle” • Data/fit-driven extraction of dynamical timescales - consistent description of data? • azimuthally-sensitive HBT • K-p correlations • short-lived resonance yields • balance functions • Summary malisa - colloquium at Duke

  3. Why heavy ion collisions? The “little bang” • Bulk properties of strongly-interacting 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 ~ ms after BB • 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 the deconfined state malisa - colloquium at Duke

  4. Stages of the collision - several timescales dN/dt 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 - colloquium at Duke

  5. uRQMD simulation of Au+Au @ s=200 GeV pure hadronic & string description (cascade) ~OK at lower energies applicability @ very high density (RHIC) unclear produces too little collective flow at RHIC courtesy uRQMD collaboration malisa - colloquium at Duke

  6. Achieving the collision experimentally STAR malisa - colloquium at Duke

  7. Measuring the ashes: 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 a midrapidity, large-acceptance hadron detector malisa - colloquium at Duke

  8. Peripheral Au+Au Collision at 130 AGeV Data Taken June 25, 2000. Pictures from Level 3 online display. malisa - colloquium at Duke

  9. Au on Au Event at CM Energy ~ 130 AGeV Data Taken June 25, 2000. malisa - colloquium at Duke

  10. 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 - colloquium at Duke

  11. 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, density • direct access to underlying physics • Works qualitatively at lower energybut always overpredicts collectiveeffects - infinite scattering limitnot valid there • freezeout when energy density fallsbelow some threshold lattice QCD input malisa - colloquium at Duke

  12. Hydro time evolution of non-central collisions • entrance-channel aniostropy in x-space pressure gradients (system response)p-space anisotropy (collective elliptic flow) • correlating observations with respect to event-wise reaction plane allows much more detailed study of reaction dynamics Equal energy density lines P. Kolb, J. Sollfrank, and U. Heinz self-quenching effect - sensitive to early pressure malisa - colloquium at Duke

  13. v2: quantifies anisotropy increases from central to peripheral collisions sensitive to EoS @ lower s Data: Azimuthal-angle distributionversus reaction plane or f  fparticle-freaction plane malisa - colloquium at Duke

  14. Very large event anisotropies seen by STAR, PHENIX, PHOBOS v2 centrality • space-momentum connection clear in multiplicity dependence • different experiments agree well • finally, we reach regime of quantitative hydro validity evidence for early thermalization • AGS & lower energies: magnitude described by hadronic cascade models • RHIC; Hydro description for central to mid-central collisions • 26% more particles in-plane than out-of-plane (even more at high pT)!! malisa - colloquium at Duke

  15. Local thermal equilibrium versus Low Density Limit SPS (s=17 GeV); Low-Density-Limit and Hydro bracket pT dependence RHIC; pt dependence quantitatively described by Hydro p p Charged particles pt dependence sensitive to early thermalization malisa - colloquium at Duke

  16. Flow Space-momentum correlations <r> = 0.6 (average flow rapidity) Assymetry (periph) : ra = 0.05 Temperature T = 110 MeV System geometry R = 13 fm (central events) Assymetry (periph event) s2 = 0.05 Time: emission duration t = emission duration Blastwave parameterization - “hydrolike source” bt R analytic description of freezeout distribution: exploding thermal source malisa - colloquium at Duke

  17. Transverse momentum spectra T  110 MeV r  0.6 PID Elliptic flow Spectra and v2 from blast wave p • T=101  24 MeV • r = 0.61  0.05 • a = 0.04  0.01 • s2 = 0.04  0.01 STAR preliminary - K- 1/mT dN/dmT (a.u.) mT - m[GeV/c2] STAR, PRL 87 182301 (2001) malisa - colloquium at Duke

  18. The other half of the story… • Momentum-space characteristics of freeze-out appear well understood • “real” model (hydro) • parameterization of real model (blastwave) • What about space-time degrees of freedom ? • Probe with two-particle intensity interferometry (“HBT”) malisa - colloquium at Duke

  19. “HBT 101” - probing source geometry Creation probability r(x,p) = U*U F.T. of pion source Measurable! p1 r1 x1 p source r(x) 1 m x2 r2 p2 5 fm malisa - colloquium at Duke

  20. “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 - colloquium at Duke

  21. 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 - colloquium at Duke

  22. 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/c in unplotted components STAR Collab., PRL 87 082301 (2001) malisa - colloquium at Duke

  23. World 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 - colloquium at Duke

  24. Hydro attempts to reproduce data long generic hydro out • KT dependence approximately reproduced correct amount of collective flow • Rs too small, Ro & Rl too big source is geometrically too small and lives/emits too long in models • Right dynamic effect / wrong space-time evolution??? the “RHIC HBT Puzzle” side malisa - colloquium at Duke

  25. “Realistic” afterburner not enough pure hydro hydro + uRQMD 1.0 STAR data 0.8 explosive space-time scenario suggested by observation not reproduced by realistic models RO/RS malisa - colloquium at Duke

  26. Now what? • “Realistic” dynamical models cannot adequately describe freeze-out distribution • Seriously threatens hope of understanding pre-freeze-out dynamics • Raises several doubts • is the data consistent with itself ? (can any scenario describe it?) • analysis tools understood? • Attempt to use data itself to parameterize freeze-out distribution • Identify dominant characteristics • Examine interplay between observables (e.g. flow and HBT) • Isolate features generating discrepancy with “real” physics models • focus especially on timescales malisa - colloquium at Duke

  27. 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 - colloquium at Duke

  28. Blastwave: radii vs pT K K pT=0.2 STAR data 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 pT=0.4 malisa - colloquium at Duke

  29. In peripheral events Start out-of-plane Evolve towards in-plane source Source shape: a measure of the freeze-out time scale Pion source geometry in peripheral events Typical evolution in the hydro world In-plane Out-of-plane Circular Time malisa - colloquium at Duke

  30. Anisotropic geometry leads to oscillations of the radii For example Rside Measuring the anisotropic shape: HBT with respect to reaction plane Out-of-plane Circular In-plane Rside2 (fm2) f (degree) fp=90° Rside (small) Rside (large) Reaction plane Naïve view with no flow fp=0° malisa - colloquium at Duke

  31. Same blastwave parameters as required to describe v2(pT,m), plus two more: Ry = 10 fm t = 2 fm/c Both p-space and x-space anisotropies contribute to R(f) mostly x-space: definitely out-of-plane calibrating with hydro, tfreezeout ~ 7 fm/c Out-of-plane extended source~ short system evolution time STAR preliminary Ros2 - new “radius” important for azimuthally asymmetric sources malisa - colloquium at Duke

  32. Smaller source  stronger (anti)correlation K-p correlation well-described by: Static sphere (no radial flow): R= 7 fm Blast wave with same parameters as spectra, HBT But with non-identical particles, we can access more information… Kaon – pion correlation:dominated by Coulomb interaction STAR preliminary malisa - colloquium at Duke

  33. 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 - colloquium at Duke

  34. clear space-time asymmetry observed C+/C- ratio described by: static (no-flow) source w/ tK- tp=4 fm/c “standard” blastwave w/ no time shift We “know” there is radial flow further evidence of very rapid freezeout 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 - colloquium at Duke

  35. A consistent picture within blastwave malisa - colloquium at Duke

  36. Consistency with other probes? tkinetic -tcharge creation (kinetic ??) tkinetic • Focussing on transverse plane, consistent picture within simple parameterization • explosive freezeout - short duration of kinetic freezeout kinetic • out-of-plane-extended shape: “short” evolution time to kinetic freezeout tkinetic • Other probes of timescales: • RL(mT): tkinetic • short-lived resonance survival: tkinetic - tchemical (kinetic ?) • Balance Functions: malisa - colloquium at Duke

  37. Rlong from HBT Kt = pair Pt Rside Rout • R.H.I.C. - strong longitudinal expansion • Rlong probes longitudinal homogeneity lengths size of region emitting a given pZ • In Bjorken picture: probe emission time tkinetic • How wide does the cell become after evolving during tkinetic? bt Rlong bl bl malisa - colloquium at Duke

  38. Simple Sinyukov formula (S. Johnson) RL2 = tkinetic2 T/mT tkinetic = 10 fm/c (T=110 MeV) B. Tomasik (~3D blast wave) tkinetic = 8 fm/c (p+p+) tkinetic = 9.2 fm/c (p-p-) From Rlong:tkinetic = 8-10 fm/c(compare ~7 fm/c from anisotropic shape) malisa - colloquium at Duke

  39. short-lived resonances K*(892) t = 3.9 fm/c (1520) t = 12.8 fm/c Rescattering of daughters between chemical and kinetic freeze-out washes out the resonance signal Sensitive to tkinetic - tchemical Resonance survival rate d1 d1 R R d2 d2 kinetic rescattering time chemical freeze out T~170 MeV thermal freeze out T~110MeV UrQMD:signal loss in invariant mass reconstruction K*(892) (1520)  SPS (17 GeV) [1] 66% 50% 26% RHIC (200GeV) [2] 55% 30% 23% malisa - colloquium at Duke

  40. Resonance reconstruction (via combinatorics):K* and L(1520) from STAR K*0 K+ + - K*0 K- + + L(1520)  p + K- minv (GeV/c2) Upper limit estimation: dN/dy preliminary (1520) |y|<1 < 1.2 at 95% C. L. multiplicity for |y| <0.5 K*0 |y|<0.5 = 10.0  0.8  25% malisa - colloquium at Duke

  41. Combining both K* and L(1520): Resonance survival rate:Rafelski’s picture Upper limit • t = tkinetic - tchemical ~ 0-3 fm/c • Caveats: • partial L “quenching” (width broadening) allows for higher T, still small t • Tchem~100 MeV ?!? • Thermal fit: T ~ 170 MeV • no evidence of low-pT suppression • Possible K* regeneration? malisa - colloquium at Duke

  42. Strong collective flow at RHIC clear from p-space observables well-described by hydro important implications for x-space observables (HBT, balance functions) Problem! - HBT systematics not reproduced by hydro right dynamic effects, but wrong evolution? analysis tools “miscalibrated,” or something wrong in model, or… systematics point to timescale Try to provide feedback to modelers... Summary • Blastwave parameterization • incorporates implicitly x-p correlations • consistent picture of several observables • central: dN/dpT, HBT(pT), K-p • 3 views of radial flow • peripheral: v2(m,pT), HBT(f) • out-of-plane extended source! • just a “toy,” but consistency suggests the x-p interplay and basic description is right • useful feedback to modelers (?) • short evolution time, ~”instant” freezout! • Other estimators of timescales • RL(mT), resonance yields**, balance fctns** • suggest timescales ~consistent with blastwave estimates ** rather different analysis/models, with several open issues malisa - colloquium at Duke

  43. Summary:Collision time scale from STAR data ~1 fm/c explosive!! Balance function (require flow) Resonance survival Rout, Rside Rlong (and HBT wrt reaction plane) ~7-10 fm/c rapid!! dN/dt time 5 fm/c 1 fm/c 10 fm/c 20 fm/c Chemical freeze out Kinetic freeze out malisa - colloquium at Duke

  44. The End malisa - colloquium at Duke

  45. Super-cooling of the QGP phase Many bubble system (M. Gyulassy) Bubble carry flow Each bubble break very rapidly Product of bubble don’t reinteract with each other Dynamical fluctuations? Brutal breaking of the chiral symmetry (A. Dumitru) Pion become off-shell and can freeze out If system has evolve long enough: no re-interaction Short emission duration Caveat: Too long lifetime? Dynamical fluctuations? Back to back p+p- correlations Some speculative ideas malisa - colloquium at Duke

  46. A way to get short emission duration pions take a long time to become on-shell and freeze-out Freeze-out a low density: no reinteractions, short emission duration Wouldn’t the system live too long? Imply back to back p+p- correlations? Dynamical fluctuations? Speculation:A. Dumitru malisa - colloquium at Duke

  47. Summary • Spectra • Very strong radial flow field superimposed on thermal motion • T saturates rapidly ~ 140 MeV •  higher at RHIC • space-momentum correlations important • “stiffer” system response? • consistent with hydro expectation • Momentum-space anisotropy • sensitive to EoS and early pressure and thermalization • significantly stronger elliptical flow at RHIC, compared to lower energy • indication of coordinate-space anisotropy as well as flow-field anisotropy (v2 cannot distinguish its nature, however) • for the first time, consistent with hydro expectation malisa - colloquium at Duke

  48. Summary (cont’) • HBT • radii grow with collision centrality R(mult) • evidence of strong space-momentum correlations R(mT) • non-central collisions spatially extended out-of-plane R(f) • The spoiler - expected increase in radii not observed • presently no dynamical model reproduces data • Combined data-driven analysis of freeze-out distribution • Single parameterization simultaneously describes • spectra • elliptic flow • HBT • K-p correlations • most likely cause of discrepancy is extremely rapid emission timescale suggested by data - more work needed! malisa - colloquium at Duke

  49. Can we learn from blasphemy? HBT R, l mT (GeV/c2) centrality • purely hadronic model, even at T = 300 MeV, r ~ 6 GeV/fm3 • details of elliptic flow and HBT ~well-reproduced • worked similarly well at SPS (impt!) T. Humanic nucl-th/0203004 malisa - colloquium at Duke

  50. A “typical” emissiontime distribution dN/dt hydro+RQMD D. Teaney malisa - colloquium at Duke

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