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Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration

Hadron Yields, Hadrochemistry, and Hadronization in High Energy Nuclear Collisions. Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration. Outline. Introduction / Motivation Statistical Model - T ch ,  B , g s Experimental Results (SPS, RHIC, …)

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Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration

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  1. Hadron Yields, Hadrochemistry, and Hadronization in High Energy Nuclear Collisions Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration

  2. Outline • Introduction / Motivation • Statistical Model - Tch, B, gs • Experimental Results (SPS, RHIC, …) • Multi-strange hadron spectra and partonic collectivity • Summary

  3. Heavy Ion Collisions Time  • 1) Initial condition: 2) System evolves: 3) Bulk freeze-out • Baryon transfer - parton/hadron expansion - hadronic dof • - ET production - inel. interactions cease: • Partonic dof particle ratios, Tch, mB • - elas. interactions cease • Paticle spectra, Tth, <bT> Plot: Steffen A. Bass, Duke University

  4. STAR

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

  6. Particle Identification (ds) (ss) (uds) (dss) (sss) Identify (multi-)strange particles in full azimuthal acceptance of STAR!

  7. Chemical Freeze-out Model Refs. J.Rafelski PLB(1991)333 P. Braun-Munzinger et al., nucl-th/0304013 Hadron resonance ideal gas Density of particle i Qi : 1 for u and d, -1 for u and d si : 1 for s, -1 for s gi:spin-isospin freedom mi : particle mass Tch : Chemical freeze-out temperature mq : light-quark chemical potential ms : strange-quark chemical potential V : volume term, drops out for ratios! gs : strangeness under-saturation factor All resonances and unstable particles are decayed Compare particle ratios to experimental data

  8. Central Collisions at RHIC Au+Au @130GeV P. Braun-Munzinger et al., nucl-th/0304013. • Particle ratios vary by factor ~100 • Statistical model reproduces data well, c2= /dof • Tch = 170  10 MeV, mB = 4010 MeV; ms = f(mB), gs 1 • Strangeness fully equilibrated at RHIC!

  9. At RHIC, Au+Au@130GeV • hadronization occurs at Tch17010 MeV • full strangeness equilibration in central collisions, gs = 1 ! Centrality Dependence* *M. Kaneta, QM2002, Nantes, France. Red: fit with multi-strange hadrons Blue: fit w/o multi-strange hadrons

  10. Beam-Energy Dependence Temperature (GeV) Chemical potential (MeV) Bombarding energies Bombarding energies With higher collision energies: Tchsaturates close to phase boundary, mB decreases  approaching net-baryon free! At RHIC, gs = 1.0 (at SPS: 0.75)  full strangeness equilibration at RHIC

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

  12. Chemical Freeze-out (cont’d) • Inelastic interactions cease at <E>/<N> = 1GeV* • At RHIC, chemical and critical conditions coincide  Inelastic interactions reduced at RHIC? Temperature (MeV) <E>/<N> = 1GeV Baryon-Chemical potential mB(GeV) *J. Cleymans and K. Redlich, Phys. Rev. Lett. 81, 5284 (1998).

  13. Resonance Ratios • K* lifetime ~ 4fm/c • K*  K + p • K*/K ratio decreases by factor two  hadronic re-scattering !  measure more resonances to study collision dynamics

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

  15. Hadron Yields • At RHIC: - chemical freeze-out close to phase boundary,Tch ~17010 MeV- approaching net-baryon free,mB = 4010 MeV- full strangeness equilibration! • AT SPS: - strangeness not fully equilibrated (gs = 0.75) • Information about pre-hadronic phase?

  16. Pressure, Flow, … • Thermodynamic identity • – entropy p – pressure U – energy V – volume t = kBT, thermal energy per dof • In A+A collisions, interactions among constituentsand density distribution lead to: pressure gradient  collective flow • number of degrees of freedom (dof) • Equation of State (EOS) • cumulative – partonic + hadronic

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

  18. Slope Parameters vs Mass • Small X-section limit: , J/y sensitive to collectivity at parton level? • At high energy, high gluon density leads to parton flow

  19. Elliptic Flow, v2 coordinate-space-anisotropy  momentum-space-anisotropy y py px x Initial/final conditions, dof, EOS

  20. Multi-Strange Baryons v2 • Multi-strange baryons show collectivity ! • Partonic collectivity at RHIC!

  21. Quark Coalescence • Exp. data consistent with quark coalescence scenario • Partonic collectivity at RHIC! • Pentaquark q+(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

  22. Summary • Statistical model describes hadron production at RHIC Tch ~17010MeV, mB = 4010 MeV • strangeness fully equilibrated • Partonic Collectivity / Quark Coalescence ! • Measure centrality dependence yields, spectra and v2of f, K*, X,W, …, D0, Ds, Lc, q+- to confirm partonic collectivity -probe thermalization

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