1 DNP03, Tucson, Oct 29, 2003

Kai Schweda

Lawrence Berkeley National Laboratory

for the STAR collaboration

Hadron Yields, Hadrochemistry,

and Hadronization in High Energy

Nuclear Collisions

2 DNP03, Tucson, Oct 29, 2003

Outline

Introduction / Motivation

Statistical Model - Tch, B, s

Experimental Results (SPS, RHIC, …)

Multi-strange hadron spectra and partonic

collectivity

Summary

3 DNP03, Tucson, Oct 29, 2003

Heavy Ion Collisions

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

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, B

- elas. interactions cease

Paticle spectra, Tth, <T>

Time

Plot: Steffen A. Bass, Duke University

4 DNP03, Tucson, Oct 29, 2003 STARSTAR

5 DNP03, Tucson, Oct 29, 2003

Collision Geometry

x

z

Non-central Collisions

Au + Au sNN = 200 GeV

Uncorrected

• No direct measure of impact parameter

• Use track multiplicity to define collision

centrality

6 DNP03, Tucson, Oct 29, 2003

Particle IdentificationParticle Identification

Identify (multi-)strange particles in full azimuthal acceptance of STAR!

(ss)(ds)

(sss)(dss)(uds)

7 DNP03, Tucson, Oct 29, 2003

Chemical Freeze-out Model

Hadron resonance ideal gas

Compare particle ratios to experimental data

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

All resonances and unstable particles are decayed

Refs. J.Rafelski PLB(1991)333P. Braun-Munzinger et al., nucl-th/0304013

Tch : Chemical freeze-out temperatureq : light-quark chemical potentials : strange-quark chemical potentialV : volume term, drops out for ratios!s : strangeness under-saturation factor

Density of particle i

8 DNP03, Tucson, Oct 29, 2003

Central Collisions at RHIC

1) Particle ratios vary by factor ~100

2) Statistical model reproduces data well, 2= /dof

3) Tch = 170 10 MeV, B = 4010 MeV; s = f(B), s 1

4) Strangeness fully equilibrated at RHIC!

P. Braun-Munzinger et al., nucl-th/0304013.

Au+Au @130GeV

9 DNP03, Tucson, Oct 29, 2003

Centrality Dependence*

At RHIC, Au+Au@130GeV

hadronization occurs at Tch 17010 MeV

full strangeness equilibration in central collisions, s = 1 !

Red: fit with multi-strange hadronsBlue: fit w/o multi-strange hadrons

*M. Kaneta, QM2002, Nantes, France.

10 DNP03, Tucson, Oct 29, 2003

Bombarding energies

Te

mp

era

ture

(G

eV

)

Ch

em

ica

l po

ten

tial (

Me

V)

Bombarding energies

Beam-Energy Dependence

With higher collision energies:

Tch 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

11 DNP03, Tucson, Oct 29, 2003

Chemical Freeze-out SystematicsChemical Freeze-out Systematics

At SPS and RHIC: hadron yields freeze-

out close to phase boundary !

Approaching net-baryon free !

Lattice QCD predictions

Neutron star

12 DNP03, Tucson, Oct 29, 2003

Chemical Freeze-out (cont’d)T

empe

ratu

re (

MeV

)

Baryon-Chemical potential B(GeV)

<E>/<N> = 1GeV

Inelastic interactions cease

at <E>/<N> = 1GeV*

At RHIC, chemical and

critical conditions coincide

Inelastic interactions

reduced at RHIC?

*J. Cleymans and K. Redlich, Phys. Rev. Lett. 81, 5284 (1998).

13 DNP03, Tucson, Oct 29, 2003

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

14 DNP03, Tucson, Oct 29, 2003

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).

15 DNP03, Tucson, Oct 29, 2003

Hadron Yields

At RHIC:

- chemical freeze-out close to phase boundary,

Tch ~17010 MeV

- approaching net-baryon free, B = 4010 MeV

- full strangeness equilibration!

AT SPS:

- strangeness not fully equilibrated (s = 0.75)

Information about pre-hadronic phase?

16 DNP03, Tucson, Oct 29, 2003

Pressure, Flow, …Pressure, Flow, …

pdVdUd Thermodynamic identity

– entropy p – pressureU – energy V – volume= 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 DNP03, Tucson, Oct 29, 2003

1) Compare to 1) Compare to , , KK, and , and p,p, multi-strange particles multi-strange particles ,, are found at higher Tare found at higher T and lower <and lower <TT>>

Collectivity prior to Collectivity prior to hadronization hadronization

2) Sudden single freeze-out*2) Sudden single freeze-out*Resonance decay lower TResonance decay lower Tfofo

for (for (, , KK, , pp)) Collectivity prior to Collectivity prior to

hadronizationhadronization

Partonic Partonic Collectivity !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

18 DNP03, Tucson, Oct 29, 2003

Slope Parameters vs Mass

gluon

tii

n

pm

00

22

-exp

Small X-section limit: , J/

sensitive to collectivity at parton level?

At high energy, high gluon density leads to parton flow

2

thermal massTSlope

19 DNP03, Tucson, Oct 29, 2003

Elliptic Flow, vElliptic Flow, v22

y

x

py

px

coordinate-space-anisotropy momentum-space-anisotropy

Initial/final conditions, dof, EOS

1i

Ritttt

))cos(i(2v1dydpp

dN

2

1

dyddpp

dN

20 DNP03, Tucson, Oct 29, 2003

Multi-Strange Baryons v2

Multi-strange baryons

show collectivity !

Partonic collectivity Partonic collectivity

at RHIC!at RHIC!

21 DNP03, Tucson, Oct 29, 2003

Quark Coalescence

Exp. data consistent with quark

coalescence scenario

Partonic collectivity at RHIC!Partonic collectivity at RHIC!

Pentaquark Pentaquark

(uudds), n=5 ?(uudds), n=5 ?

Z. Lin et al., PRL, 89, 202302(02)R. Fries et al., nucl-th/0301087D. Molnar et al. nucl-th/0302014

22 DNP03, Tucson, Oct 29, 2003

Summary

Statistical model describes hadron production at RHIC

Tch ~17010MeV, B = 4010 MeV

strangeness fully equilibrated

Partonic Collectivity / Quark Coalescence !

Measure centrality dependence yields, spectra and v2

of , K*, , , …, D0, Ds, c,

to confirm partonic collectivity

probe thermalization