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XXXIII International Symposium on Multiparticle Dynamics, September 7, 2003 Kraków, Poland Manuel Calderón de la Barca Sánchez STAR Collaboration Review of Spectra at RHIC

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2 Outline @ First of all, there’s too much data!! H Focus on some recent results and analyses @ BRAHMS @ PHOBOS @ PHENIX @ STAR H Low, Intermediate, High-p t @ Can we understand it? Can at least some of it be synthesised? H Spectra H Flow

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3 Particle Spectra in Au+Au, STAR |y|<.5 Hydro inspired “Thermal” Fits (input to Blast-Wave parameterization) (T, t ) = (170 MeV, 0.6c) Large transverse flow component in central collisions. STAR Preliminary

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4 Hydrodynamics Equation of State @ Low p t, 99.5% of particles are below 2 GeV. Hydrodynamics describes bulk particle momentum distributions Hydro is limit of zero mean free path…early phase dominated by strong interactions? Calculations too long a system lifetime (still work to do) Enormous initial pressure, but decouples quickly (~10 fm/c)

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5 Spectra at large y, BRAHMS. y=3 Thermal fit T = 0.42 T = 140 MeV y=0 Thermal fit T = 0.53 T = 138. MeV y=3 Radial flow decreases at large rapidity. Boost invariant region is only about 1 unit wide! 3-D hydro

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6 Charged hadrons at large , PHOBOS T. Hirano Hydrodynamics: Mid-rapidity data is well described, but larger rapidity is not.

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7 Particle Ratios and Statistical Models Statistical models do a very good job. Values T ch are very close to expected T crit from lattice. However, this alone cannot prove a phase transition nor that the system is thermal; but coupled with agreement from hydrodynamics (spectra and v 2 ), evidence starts to increase…

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8 Intermediate p t, spectra for various masses Yield of p ( ) similar to (K) at ~3 GeV, flow effect for heavier particle/baryon?

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9 Compare with scaling by N coll … K 0 s and 0 show suppression at 2-3 GeV, p and do not… strong radial flow for heavier particles?

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10 Particles with Similar Mass @ Differ at low pt, similar at ~3 GeV @ Reflection of Flow? Rescattering? Recombination? @ Rescattering has effect on other observables: resonances! (See Patricia’s talk)

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11 Wealth of data! @ It is very important to try to understand as much of the combined measurements as possible H Under a single framework! @ Many times, predictions work for observable A but fail for observable B. Need a coherent picture! @ Some recent ideas: H Hydro-inspired Blast-wave (won’t go into it) H Recombination+Fragmentation H Single Freeze-out

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12 Fragmentation + Recombination Fragmentation Recombination Bass et al. nucl-th/0306027 Lopez, Parikh, Siemens, PRL 53 (1984) 1216: Net charge and baryon number fluctuations [Asakawa, Heinz, BM, PRL 85 (2000) 2072; Jeon, Koch, PRL 85 (2000) 2076] Balance functions [Bass, Danielewicz, Pratt, PRL 85 (2000) 2689] Recombination / coalescence [Fries, BM, Nonaka, Bass, nucl-th/0301087; Greco, Ko, Levai, nucl-th/0301093; Molnar, Voloshin, nucl-th/0302014]

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13 F+R: Model assumptions @ at low p t, quarks and antiquarks recombine into hadrons locally “at an instant”: @ hadron momentum P is much larger than average momentum Δp 2 of the internal quark wave function of the hadron; features of the parton spectrum are shifted to higher p t in the hadron spectrum @ parton spectrum has thermal part (quarks) and a power law tail (quarks and gluons) from pQCD.

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14 Does it fit the measured spectra? T eff = 350 MeV blue- shifted temperature pQCD spectrum shifted by 2.2 GeV R.J. Fries, B. Müller, C. Nonaka, S.A. Bass; PRL 90 202303 (2003)

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15 For identified particles… , K

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16 …p, , , ,

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17 Ratios vs p t

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18 High p t suppression. Reproduces charged hadron suppression, and flavor dependence. Prediction, quenching for protons above 6 GeV, where fragmentation starts to dominate

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19 What about v 2 ?

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20 Does v 2 reflect partonic flow? Recombination model suggests that hadronic flow reflects partonic flow (n = number of valence quarks): Provides measurement of partonic v 2 ! P. Sorensen (UCLA – STAR) Quark v 2 See also: Lin & Ko, PRL 89 (2002) 202302; Molnar & Voloshin, nucl-th/0302014

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21 Identified Particle Spectra at RHIC @ 200 GeV Feed-down matters !!! BRAHMS: 10% central PHOBOS: 15% PHENIX: 5% STAR: 5%

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22 Single freeze-out model, T ch = T kin ? W. Broniowski and W. Florkowski, PRC 65 064905 (2002), for 130 GeV A. Baran, W. Broniowski, W. Florkowski nucl-th/0305075 for 200 GeV ratios and spectra. Very nice feature, include feeddown in the calculations. Describe spectra and ratios vs p t and vs centrality well Supports the use of thermal approach to heavy ion collisions If T ch =T kin, very explosive expansion!

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23 High-p t : Latest news from the d+Au run @ In Au+Au, suppression of high-pt hadrons and of away side jet, not seen in d+Au. Final state effect…consistent with the production of dense matter!! From cover of PRL 91 (2003) 072302 Phobos 072303 Phenix 072304 Star 072305 Brahms

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24 Summary & Conclusions @ All 4 RHIC experiments have continued their outpour of measurements. @ Low pt spectra, hydrodynamic fits, statistical models taken together yield support (albeit don’t prove) to a high density thermalized phase. H Still trouble in the longitudinal direction (HBT, v 2 vs y) @ We are beginning to see more theoretical efforts that encompass various observables! That is good! H Spectra, flow, correlations. Would like to understand in one picture, p t, y and centrality dependence. W Fragmentation + Recombination: aplicability of the recombination regime to 3-6 GeV, fragmentation dominates at a higher p t than one naïvely expected. W v 2 of hadrons reflects v 2 of constituent quarks (? and !) @ High-pt spectra and correlations: suppression of hadrons and away-side jet is a final state effect.

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