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DNP03, Tucson, Oct 29, 2003 1 Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration Hadron Yields, Hadrochemistry, and Hadronization in High Energy Nuclear Collisions

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DNP03, Tucson, Oct 29, 2003 2 Outline Introduction / Motivation Statistical Model - T ch, B, s Experimental Results (SPS, RHIC, …) Multi-strange hadron spectra and partonic collectivity Summary

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DNP03, Tucson, Oct 29, 2003 3 Heavy Ion Collisions 1) Initial condition:2) System evolves:3) Bulk freeze-out -Baryon transfer- parton/hadron expansion- hadronic dof - E T production- inel. interactions cease: -Partonic dof particle ratios, T ch, B - elas. interactions cease Paticle spectra, T th, Time Plot: Steffen A. Bass, Duke University

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DNP03, Tucson, Oct 29, 2003 4 STAR

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5 Collision Geometry x z Non-central Collisions Au + Au s NN = 200 GeV Uncorrected No direct measure of impact parameter Use track multiplicity to define collision centrality

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DNP03, Tucson, Oct 29, 2003 6 Particle Identification Identify (multi-)strange particles in full azimuthal acceptance of STAR! (ss) (ds) (sss)(dss)(uds)

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DNP03, Tucson, Oct 29, 2003 7 Chemical Freeze-out Model Hadron resonance ideal gas Compare particle ratios to experimental data Q i : 1 for u and d, -1 for u and d s i : 1 for s, -1 for s g i : spin-isospin freedom m i : particle mass All resonances and unstable particles are decayed Refs. J.Rafelski PLB(1991)333 P. Braun-Munzinger et al., nucl-th/0304013 T ch : Chemical freeze-out temperature q : light-quark chemical potential s : strange-quark chemical potential V: volume term, drops out for ratios! s : strangeness under-saturation factor Density of particle i

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DNP03, Tucson, Oct 29, 2003 8 Central Collisions at RHIC 1)Particle ratios vary by factor ~100 2)Statistical model reproduces data well, 2 = /dof 3)T ch = 170 10 MeV, B = 40 10 MeV; s = f( B ), s 1 4)Strangeness fully equilibrated at RHIC! P. Braun-Munzinger et al., nucl-th/0304013. Au+Au @130GeV

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DNP03, Tucson, Oct 29, 2003 9 Centrality Dependence* At RHIC, Au+Au@130GeV hadronization occurs at T ch 170 10 MeV full strangeness equilibration in central collisions, s = 1 ! Red: fit with multi-strange hadrons Blue: fit w/o multi-strange hadrons *M. Kaneta, QM2002, Nantes, France.

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DNP03, Tucson, Oct 29, 2003 10 Bombarding energies Temperature (GeV) Chemical potential (MeV) Bombarding energies Beam-Energy Dependence With higher collision energies: T ch saturates close to phase boundary, B decreases approaching net-baryon free! At RHIC, s = 1.0 (at SPS: 0.75) full strangeness equilibration at RHIC

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DNP03, Tucson, Oct 29, 2003 11 Chemical Freeze-out Systematics At SPS and RHIC: hadron yields freeze-out close to phase boundary ! Approaching net-baryon free ! Lattice QCD predictions Neutron star

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DNP03, Tucson, Oct 29, 2003 12 Chemical Freeze-out (cont’d) Temperature (MeV) Baryon-Chemical potential B (GeV) / = 1GeV Inelastic interactions cease at / = 1GeV* At RHIC, chemical and critical conditions coincide Inelastic interactions reduced at RHIC? *J. Cleymans and K. Redlich, Phys. Rev. Lett. 81, 5284 (1998).

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DNP03, Tucson, Oct 29, 2003 13 Resonance Ratios K* lifetime ~ 4fm/c K* K + K*/K ratio decreases by factor two hadronic re- scattering ! measure more resonances to study collision dynamics

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DNP03, Tucson, Oct 29, 2003 14 Elementary p+p Collisions Low multiplicities use canonical esemble Strangeness has to be conserved locally particle yields are well reproduced Strangeness not equilibrated ! ( s = 0.5) Statistical Model Fit: F. Becattini and U. Heinz, Z. Phys. C 76, 269 (1997).

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DNP03, Tucson, Oct 29, 2003 15 Hadron Yields At RHIC: - chemical freeze-out close to phase boundary, T ch ~170 10 MeV - approaching net-baryon free, B = 40 10 MeV - full strangeness equilibration! AT SPS: - strangeness not fully equilibrated ( s = 0.75) Information about pre-hadronic phase?

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DNP03, Tucson, Oct 29, 2003 16 Pressure, Flow, … Thermodynamic identity – entropy p – pressure U – energy V – volume = k B T, thermal energy per dof In A+A collisions, interactions among constituents and density distribution lead to: pressure gradient collective flow number of degrees of freedom (dof) Equation of State (EOS) cumulative – partonic + hadronic

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DNP03, Tucson, Oct 29, 2003 17 1) Compare to , K, and p, multi-strange particles , multi-strange particles , are found at higher T are found at higher T and lower and lower Collectivity prior to hadronization 2) Sudden single freeze-out* Resonance decay lower T fo for ( , K, p) Collectivity prior to hadronization Partonic Collectivity ! Partonic Collectivity ! Kinetic Freeze-out Data: Data: STAR preliminary Au+Au@200GeV: Nucl. Phys. A715, 129c(2003). *A. Baran, W. Broniowski and W. Florkowski; nucl-th/0305075

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DNP03, Tucson, Oct 29, 2003 18 Slope Parameters vs Mass Small X-section limit: , J/ sensitive to collectivity at parton level? At high energy, high gluon density leads to parton flow

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DNP03, Tucson, Oct 29, 2003 19 Elliptic Flow, v 2 y x pypy pxpx coordinate-space-anisotropy momentum-space-anisotropy Initial/final conditions, dof, EOS

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DNP03, Tucson, Oct 29, 2003 20 Multi-Strange Baryons v 2 Multi-strange baryons show collectivity ! Partonic collectivity at RHIC! Partonic collectivity at RHIC!

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DNP03, Tucson, Oct 29, 2003 21 Quark Coalescence Exp. data consistent with quark coalescence scenario Partonic collectivity at RHIC! Pentaquark (uudds), n=5 ? Pentaquark (uudds), n=5 ? Z. Lin et al., PRL, 89, 202302(02) R. Fries et al., nucl-th/0301087 D. Molnar et al. nucl-th/0302014

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DNP03, Tucson, Oct 29, 2003 22 Summary Statistical model describes hadron production at RHIC T ch ~170 10MeV, B = 40 10 MeV strangeness fully equilibrated Partonic Collectivity / Quark Coalescence ! Measure centrality dependence yields, spectra and v 2 of , K*, , , …, D 0, D s, c, to confirm partonic collectivity probe thermalization

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