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

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

DNP03, Tucson, Oct 29, 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

DNP03, Tucson, Oct 29, STAR

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

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

DNP03, Tucson, Oct 29, 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/ 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

DNP03, Tucson, Oct 29, 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/

DNP03, Tucson, Oct 29, Centrality Dependence* At RHIC,  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.

DNP03, Tucson, Oct 29, 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

DNP03, Tucson, Oct 29, 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

DNP03, Tucson, Oct 29, 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).

DNP03, Tucson, Oct 29, 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

DNP03, Tucson, Oct 29, 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).

DNP03, Tucson, Oct 29, 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?

DNP03, Tucson, Oct 29, 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

DNP03, Tucson, Oct 29, ) 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 Nucl. Phys. A715, 129c(2003). *A. Baran, W. Broniowski and W. Florkowski; nucl-th/

DNP03, Tucson, Oct 29, 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

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

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

DNP03, Tucson, Oct 29, 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, (02) R. Fries et al., nucl-th/ D. Molnar et al. nucl-th/

DNP03, Tucson, Oct 29, 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