Strangeness thermalization at RHIC – partonic or hadronic ?

Rene Bellwied Wayne State University

20th Winter Workshop on Nuclear Dynamics

Montego Bay, March 15th -20th , 2004

1.) strangeness yields - enhancementschemical equilibration, saturation,

equilibrationhow do we compare pp, dA, AA properly ?

2.) strangeness spectra - dynamicskinetic equilibration, flow, suppression, fragmentation, recombinationhow do we compare pp, dA, AA properly ?

Elliptic (anisotropic) Flow for a mid-peripheral collision – a strong indicator of collectivity

Dashed lines: hard sphere radii of nuclei

Reactionplane

In-planeOu

t-o

f-p

lan

e

Y

X

Re-interactions FLOW Re-interactions among what? Hadrons, partons or both?

In other words, what equation of state?

Flow

Flo

w

...) φ) ( v ) (φ v (dy dpN d

dφ dy dpN d

t t

2 2 2 121

2 1

2 3

cos cosπ

Directed flow Elliptic flow

v2 (anisotropy, squeeze-out) measurements

System deformation in HBT

• Final state eccentricity from– v2

– HBT with respect to reaction plane

• Conclusions:– System was still deformed

at freezeout

– System froze out EARLY

Y

XTime

22

22

xy

xy

Tim

e

Consequences of a strong v2 at RHIC

1.) v2 is strong and has to come from very early time after collision. Hadronic v2 is not sufficient in terms of magnitude and timescale2.) v2 is very well described by hydrodynamics (fluid dynamics). 3.) if the phase producing the flow is partonic then we have partonic fluid (dissipative, strongly interacting, small correlation length) rather than a plasma (large correlation length, weakly interacting quasi-particle gas).

(nucl-th/0403032)

New phase diagrams for RHIC

Shuryak, QM04

deconfinement

restoration

partonfluid(pre-hadrons)

Cassing, 2004

A strongly interacting parton liquid

Bulk properties seemingly well described by:

- dynamical hydrodynamics- single freeze-out surface blast wave parametrization- thermal freeze-out models

Are there other signatures of a bulk partonic liquid in strangeness production or strangenesskinematics ? Is this liquid thermalized ?

Strangeness chemistry: beautiful agreement with statistical chemical

equilibration model for non-resonant particles

Strangeness enhancement:Wroblewski factor evolution

Wroblewski factor

dependent on T and B

dominated by KaonsLines of constant S

<E>/<N> = 1 GeV

I. Increase instrange/non-strangeparticle ratiosII. Maximum isreached

III. Ratios decrease(Strange baryonsaffected more stronglythan strange mesons)

Peaks at 30 A GeV in AA collisions due to strong B dependence

mesons

baryons

hidden strangeness mesons

PBM et al., hep-ph/0106066

total

RHIC fixedtarget mode(internal gas target)K

/K

+/

[GeV]

Does the thermal model always work ?

Resonance ratios not well described Reaction dynamics

Dat

a –

Fit

()

Rat

io

see talk by C.Markert

The switch from canonical to grand-canonical(Tounsi,Redlich, hep-ph/0111159, hep-ph/0209284)

The strangeness enhancement factors at the SPS (WA97) can be explained as a suppression in pp rather than an enhancement in AA.In pp the phase space for particle production is small. The small volume term will dominate the canonical ensemble (suppression) whereasin AA the volume and strangeness content is large (grand-canonical)

Plots of canonical suppression

equilibration volume ?

Tounsi et al.

Strangeness enhancement factors at RHIC

Npart-scaling in Au-Au at RHIC -> lack of Npart scaling = no thermalization ?

Alternatives: no strangeness saturation in peripheral collisions (s = 1)

non-thermal jet contributions rise with centrality

Grandcanonical prediction

Non –thermal jet contributions ? jet contributions scale with Nbin

around 20% of the multistrange yield is above 2 GeV/c at RHIC

(little centrality and baryon dependence)

from 2 GeV/c on all strange baryon spectra scale with Nbin

%geo <Npart> <Nbin> <Nbin/Npart>

0-5 352 (67) 990.0 (69

77) 2.85 (0.17)

5-10 298 (1010) 783.7 (71

74) 2.65 (0.17)

10-20 232 (1110) 563.2 (64

59) 2.43 (0.17)

20-30 165 (1312) 355.0 (53

49) 2.14 (0.17)

30-40 114 (1312) 213.9 (41

36) 1.86 (0.16)

40-60 61 (1010) 91.8 (22

23) 1.44 (0.14)

60-80 19.8 (56) 20.0 (7

9) 0.96 (0.10)

Corrected strangeness enhancement factors

< 2 GeV/cNpart scaling>2 GeV/cNbin scaling

Let’s fit spectra: kinetic equilibration

Mass dependence of the transverse expansion, which is well described by thermal and hydrodynamics models

preliminary preliminary

Blastwave: a hydrodynamic inspired description of spectra

s

Ref. : Schnedermann, Sollfrank & Heinz,PRC48 (1993) 2462

Spectrum of longitudinal and transverse boosted thermal source:

r

n

sr

TTT

TT

R

rr

T

mK

T

pImdrr

dmm

dN

tanh rapidity)(boost angleboost and

)( ondistributi velocity transverse

with

cosh

sinh

1

R

0 10

Static Freeze-out picture,No dynamical evolution to freezeout

R

Blastwave vs. Hydrodynamics

Tdec = 100 MeV

Kolb and Rapp,PRC 67 (2003)

044903.

Mike Lisa (QM04): Use it don’t abuse it ! Only use a static freeze-out parametrization when the dynamic model doesn’t work !!

,

,K,P,

STAR preliminary

Radial flow & thermalization from <pt>?

STAR preliminary

<pt> in pp = <pt> in AA for and heavier particles. No partonic flow necessary to explain <pt> in AA ? What is the origin of <pt> in pp ? Same production mechanisms than in AA ?

STAR <pt> for Nch in pp, dA, AAEnergy density in high mult. pp above critical density ??Can one even speakabout energy density in pp ?

Is pp governed by adifferent mechanism,e.g. jet fragmentation ?

Is there a <pt> saturationvalue or is this just an accident because we haveno stats for high mult pp ?

How big an effect ??

High multiplicity bias in strange particles ?

Contributions to the effective temperature

1.) basic thermal slope (similar to pp ?)(might be very jet fragmentation dependent)heavier primary particles and decaying particles

come from more energetic jet fragmentation ?

2.) hadron gas expansion

3.) parton fluid expansion

4.) Cronin effect: Initial state rescattering pushes spectrum to higher pt in pA collisions ?

Let’s look at Cronin at RHIC

Cronin = initial state effect (but now measured by HERMES in eA ??)

Lower Energy Cronin data

• Ratio of per nucleon cross sections for p+W and p+Be collisions at √s=38.8 GeV – Enhancement varies with pT

and with particle species– Cronin increases slope mimics expansion ?– Is there a sum rule ? Depletion at low momentum

equals enhancement at higher momentum ?

pT GeV/c

PRL 68, 452 (1992) Straub et al.

Energy dependence of Cronin (data)

√s

• Cronin enhancement decreasing with increasing √s

• Certainly for , K• Trend less clear for proton?

RW

/Be

PRL 68, 452 (1992) Straub et al.

Energy dependence of Cronin (theory)(Cassing, Gallmeister, Greiner (hep-ph/0311358))

• Cronin enhancement decreasing with increasing √s but still sizeable at RHIC• bigger effect for baryons than for mesons because ‘more’ partonscan rescatter in the initial phase (3 instead of 2) – recombination ?

Cronin in STAR and PHENIX(Spiros and Julia’s talks)

STAR Preliminary

Rd

Au

h±

K0s proton K±

Only statistical errors shown for

√s

STAR anti-proton spectra in pp, dA, AA

Cronin effect seems small !

L.Molnar

Physics Conclusions• We have a strongly collective, likely partonic, phase based on the

multistrange baryon elliptic flow measurements (parton liquid ?).• It is likely that global (chemical and kinetic) thermalization is

reached at all centralities, but simple enhancement plots show effects of non-thermal jet contributions.

• pp and dA are not good reference systems for kinematic quantities such as <pt> and radial flow, because non-thermal contributions such as jets and Cronin effect mimic global expansion patterns. A kinematic ‘minimum bias’ pp measurement has to be evaluated differently for each particle species. In that sense Npart is an inappropriate scaling variable, also because any non-thermal contributions do not scale with Npart

• Yields and ratios as well as the kinematics of the multi-strange baryons seem to indicate a thermalization of the early phase of the reaction.

Whatever you believe,don’t trust this man !!!!

Because it’s really a fluid,Baby !!

The national flowerof Jamaica, Maaan