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ISMD ‘02, Alushta, Ukraine Sep 9, 2002
Manuel Calderón de la Barca Sánchez
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Understanding “Bulk” Matter in HI collisions
Studying Matter: Global Observables Nch, ET, pT e, S, … Particle Yields & Ratios Tch, mB, mS, … Particle Spectra Tfo, flow, stopping, … 99.5% STAR preliminary
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Nch: Centrality Dependence at RHIC (SPS)
PHOBOS Au+Au |h|<1 200 GeV 130 GeV Au+Au _ pp 19.6 GeV preliminary (preliminary) pp not in fit fix point 1.5 off beam-rapidity Everything counts: Nch|h=0 described nicely by Kharzeev-Nardi (hard + soft) Nch scales with Npart
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ET/ Nch from SPS to RHIC
PHENIX preliminary PHENIX preliminary Hagedorn Independent of centrality Independent of energy Surprising fact: SPS RHIC: increased flow, all particles higher pT still ET/ Nch changes very little Does different composition (chemistry) account for that?
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pT of Charged Hadrons from SPS to RHIC
increase only ~2% STAR preliminary Saturation model: J. Schaffner-Bielich, et al. nucl-th/ D. Kharzeev, et al. hep-ph/ Many models predict similar scaling (incl. hydro) Need data around s = 70 GeV to verify (or falsify)
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Ratios Huge amount of results from all 4 RHIC experiments:
systematic studies of: p-/p+, K-/K+, p/p,/ ,/,/, p/p, K/p , /, /h, , /p, f/K, K*/K, … many as function of pT, Npart at s of (20), 130, and 200 GeV Problem: with and without feed-down correction BRAHMS large y coverage and reach to high pT PHENIX reach to high pT STAR multi-strange baryons
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Ratios at RHIC I : vs. p^ All experiments: p-/p+ 1 K-/K+ 0.95
3x more protons produced than shifted in from beam Does p/p also stay constant, or does it begin falling?
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Ratios at RHIC II: vs. y At mid-rapidity: Net-protons: dN/dy 7
BRAHMS 200 GeV At mid-rapidity: Net-protons: dN/dy 7 proton yield: dN/dy 29 ¾ of all protons from pair-production
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K-/K+ and p/p from AGS to RHIC
Slightly different view of statistical model. Becattini calculation using statistical model: T=170, gs=1 (weak dependency) vary mB/T K+/K- andp/p K- /K+=(p/p)1/4 is a empirical fit to the data points K-/K+ driven by ms ~ exp(2ms/T) p/p driven by mB ~ exp(-2mB/T) ms = ms (mB) since <S> = 0 Kristoph Redlich : two different curves: AGS K/K driven by associate production / RHIC pair production BUT: Holds for y 0 (BRAHMS y=3)
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Rapidity Spectra: Boost-Invariance at RHIC ?
D. Ouerdane (BRAHMS)
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Boost-Invariance at RHIC ?
p- p- MB fits dN/dy of pions looks boost-invariant BUT change in slopes for rapidity already from 0 1 BRAHMS (J.H. Lee): no change in proton slope from y = 0 BUT increase in dN/dy Boost invariance only achieved in small region |y|<0.5
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Identified Particle Spectra at RHIC @ 200 GeV
BRAHMS: 10% central PHOBOS: 15% PHENIX: 5% STAR: 5% Feed-down matters !!!
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Interpreting the Spectra
The shape of the various particle spectra teach us about: Kinetic freeze-out temperatures Transverse flow The stronger the flow the less appropriate are simple exponential fits: Hydrodynamic models (a la Heinz/Kolb/Shuryak/Huovinen/Teaney) Hydro inspired parameterizations (Blastwave) Blastwave parameterization: Ref. : E.Schnedermann et al, PRC48 (1993) 2462 (modifications by Snellings, Voloshin) Very successful in recent months Spectra HBT (incl. the Rout/Rside puzzle) Flow 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 spectra (p) HBT b
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Blastwave Fits at 130 & 200 GeV 200 GeV
Results depend slightly on pT coverage STAR: Tfo ~ 100 MeV bT ~ 0.55c (130) & 0.6c (200) PHENIX: Tfo ~ 110 MeV (200) bT ~ 0.5c (200) 200 GeV Fits M. Kaneta (STAR)
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What flows and when? STAR <pT> prediction with Tth
and <b> obtained from blastwave fit (green line) STAR <pT> prediction for Tch = 170 MeV and <b>=0 pp no rescattering, no flow no thermal equilibrium preliminary F. Wang fit k, pi, p only <pt> Boltzman for pion, K exp, p exponential, rest is exponential and appear to deviate from common thermal freeze-out Smaller elast? Early decoupling from expanding hadronic medium? Less flow? What about partonic flow?
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Does it flow? Fits to Omega mT spectra
STAR preliminary RHIC SPS/NA49 bT is not well constrained ! What do we now about elast of and ? May be it flows, and may be they freeze out with the others Maybe and are consistent with a blastwave fit at RHIC Need to constrain further more data & much more for v2 of
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Other Attempts: The Single Freeze-Out Model
Single freeze-out model (Tch=Tfo) (W. Broniowski et. al) fit the data well (and reproduce f, K*, L, X, W) Thermal fits to spectra are not enough to make the point. To discriminate between different models they have to prove their validity by describing: Spectra (shape & yield) Correlations (HBT, balance function, etc.) Flow Only then we can learn …
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Conclusions Flood of data from SPS & RHIC new probes
correlations between probes higher statistics & precision Models (Generators) are behind The majority of models in RHI fail already describing global observables (possible exception AMPT) Many models describe “A” well but fail badly at “B” can still be useful but limited scope We learn more by combing various pieces and putting them into context Thermalization, Chemical and Kinetic Freeze-out Conditions, and System Dynamics can only be studied (and are studied) using all the pieces together Agreement between thermal fits to particle spectra and ratios + flow makes a very strong case for thermalization of matter created at RHIC
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