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Recent results from STAR

Recent results from STAR. M.A. Lisa, for the STAR Collaboration. Outline. Year-1 data (Au+Au s=130 GeV) hadro-chemistry driving dynamical physics and consistent picture @ low p T ? central collisions radial flow two-particle correlations  HBT K- correlations balance functions

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Recent results from STAR

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  1. Recent results from STAR M.A. Lisa, for the STAR Collaboration

  2. Outline • Year-1 data (Au+Au s=130 GeV) • hadro-chemistry • driving dynamical physics and consistent picture @ low pT? • central collisions • radial flow • two-particle correlations •  HBT • K- correlations • balance functions • non-central collisions • elliptical flow • HBT vs reaction-plane • low-pT summary • driving physics @ “high” pT? • spectra compared to pp collisions • elliptical flow • two-particle correlations • Summary

  3. 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  + 

  4. Vector meson production in Ultra-peripheral collisions Au g Signal region: pT<0.15 GeV qq Au r0 PT • b > 2R  electromagnetic interactions • d/dpT consistent with predictions for coherent 0 production r0

  5. 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

  6. Statistical Thermal Model: Fit Results • b driven by p/p, K-/K+ • T driven by p/p

  7. Something different vs pT?Particle/Antiparticle Ratios STAR Preliminary see talk by B. Norman Within the errors no or very small pT dependence (as one might expect from simply flow)

  8. pT spectra: Flavor Dependence Enhancement at ~2 GeV is not specific to baryons  mass effect (simplest explanation: radial flow)

  9. Thermal motion superimposed on radial flow Hydro-inspired “blast-wave” thermal freeze-out fits to p, K, p, L preliminary Tth = 107 ± 8 MeV hydro predictions reproduce early pT spectra Fits by M. Kaneta

  10. Hydro attempts to reproduce data generic hydro Rlong: model waits too long before emitting Rout model emission timescale too long • KT dependence approximately reproduced correct amount of collective flow • Right dynamic effect / wrong space-time evolution??? the “RHIC HBT Puzzle” Rside

  11. 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 blastwave: R=13.5 fm, tfreezeout=1.5 fm/c pT=0.4

  12. Simple Sinyukov formula (S. Johnson) 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

  13. 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 correlation:dominated by Coulomb interaction STAR preliminary

  14. 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)

  15. 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

  16. Balance functions: How they work For each charge +Q, there is one extra balancing charge –Q. Charges: electric, strangeness, baryon number Bass, Danielewicz, Pratt (2000)

  17. Balance functions - clocking the evolution Bjorken (narrow) Pythia (wide) Model predictions • Wide  early creation of charges • nn, e+e- collisions • Narrow  late hadronization / (Q)GP • central collisions @ RHIC? Bass, Danielewicz, Pratt (2000)

  18. Balance Functions in STAR  Pairs STAR Preliminary STAR Preliminary • Peripheral collisions approach Hijing (NN) • Clear narrowing for central collisions • In Bass/Danielewicz/Pratt model, central data consistent with: • Tchem ~ 175 MeV Tkinetic ~ 110 MeV • tchem = 10 fm/c tkinetic = 13 fm/c

  19. Noncentral collision dynamics hydro evolution • hydro reproduces v2(pT,m) @ RHIC for pT < ~1.5 GeV/c • system response (pressure): x-space  p-space anisotropy • again: correct p-space dynamical effect • freezeout shape  evolution duration? v2 0.2 0.1 STAR preliminary see talk of J. Fu 0 flow of neutral strange particles PID beyond pT=1 GeV/c 0 1 3 2 pT (GeV/c)

  20. Blast-wave fit to low-pT v2(pT,m) STAR, PRL 87 182301 (2001) • spatial anisotropy indicated • consistent with out-of-plane extended source(but ambiguity exists) fp=90° Rside (small) Rside (large) • possible to “see” via HBT relative to reaction plane? • expect • large Rside at 0 • small Rside at 90 2nd-order oscillation fp=0°

  21. 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

  22. Low-pT dynamics — one (naïve?) interpretation:rapid evolution and a “flash” RHIC 130 GeV Au+Au K-p K* yield Disclaimer: all numbers (especially time) are approximate

  23. Physics at “high” pT (~6 GeV/c) leading particle hadrons q q hadrons Jet 2 leading particle leading particle suppressed y Jet 1 hadrons q q x hadrons leading particle suppressed Jets modified in heavy ion collisions -Parton Energy loss in dense nuclear medium -Modification of fragmentation function 1) high-pT suppression relative to NN (especially in central collisions) 2) finite, non-hydro v2 due to energy loss (non-central collisions) see talk of J. Klay

  24. Inclusive spectra preliminary Statistical errors only

  25. Power law fits • Power Law: “pQCD inspired” • Fits wide range of hadronic spectra: ISR Tevatron • Good fits at all centralities (2/ndf~1) • Smooth dependence on centrality • most peripheral converges to Nucleon-Nucleon reference (UA1) STAR preliminary (p0, n highly correlated)

  26. low pT scales as <Npart> preliminary • Central collisions: suppression of factor 3 (confirms PHENIX) • Peripheral collisions: “enhancement” consistent with zero(uncertainties due to <Nbinary> and NN reference) • Smooth transition central  peripheral

  27. Azimuthal anisotropy - theory and data Jet 2 y Jet 1 x Low pT: parameterized hydro High pT: pQCD with GLV radiative energy loss • finite energy loss  finite v2 at high pT • sensitive to gluon density Preliminary model: Gyulassy, Vitev and Wang, (2001) • pT<2 GeV: good description by hydrodynamics • pT>4 GeV: hydro fails but finite v2

  28. V2 centrality dependence Preliminary all centralities: finite v2 at high pT

  29. But are we looking at jets? - 2 Particle Correlations • Trigger particle pT>4 GeV/c, ||<0.7 • azimuthal correlations for pT>2 GeV/c • short range  correlation: jets + elliptic flow • long range  correlation: elliptic flow •  subtract correlation at |1- 2|>0.5 • NB: also eliminates the away-side jet correlations • extracted v2 consistent with reaction-plane method • what remains has jet-like structure first indication of jets at RHIC! 0-11% preliminary

  30. STAR vs UA1 UA1: Phys. Lett. 118B, 173 (1982) (most events from high ET trigger data) preliminary • UA1: very similar analysis (trigger pT>4 GeV/c) • But sqrt(s)=540 GeV, ||<3.0

  31. Brief Summary • chemistry: • wide range of particle yields well-described by thermal model • Tchem ~ 170 MeV b ~ 45 MeV • pT dependence of yields (e.g. baryon dominance) consistent with radial flow • dynamics at pT < 2 GeV/c • “real” model (hydro) reproduces flow systematics, but not HBT • finger-physics analysis of probes sensitive to time: • short system evolution, then emission in a flash • Tchem ~ 170 MeV Tkin ~ 110 MeV • tchem ~ 10 fm/c tkin ~ 13 fm/c • naïve? unphysical? useful feedback to modelers? • dynamics at pT > 2 GeV/c • hydro picture breaks down • preliminary jet signal observed • evidence for medium effects at high pT

  32. THE END

  33. Ratios driving the thermal fits Plots from D. Magestro, SQM2001

  34. Blast Wave Mach I - central collisions b s 1/mt dN/dmt A Tfo R mt flow profile selected (t =s (r/Rmax)n) s Ref. : E.Schnedermann et al, PRC48 (1993) 2462 t 2-parameter (Tfo, bt) fit to mT distributions

  35. 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 Mach II - Including asymmetries bt R analytic description of freezeout distribution: exploding thermal source

  36. Comparison to Hijing Ratio of integrals over correlation peak: 1.3 Hijing fragmentation is independent of quenching

  37. High-pT highlights Qualitative change at 2 GeV Jet-like structure

  38. 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

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