Helen Caines Yale University Gordon Research Conference – New London, NH– June 2006 Collisions at RHIC are very strange Outline Bulk matter Equilibrium

Helen CainesYale University

Gordon Research Conference – New London, NH– June 2006

Collisions at RHIC are very strange

Outline

• Bulk matter

• Equilibrium• Enhancement

• Beyond the bulk• Intermediate pT

Helen Caines

GRC – New London - June 2006 2

RHIC - a strange particle factory

200 GeV Au+Au

ssssss200 GeV Au+Auudss200 GeV Au+Au dssss200 GeV Au+Au

62 GeV Au+Au 62 GeV Au+Au62 GeV Au+Au

200 GeV p+p 200 GeV p+p

(u (us+s+ddss))

( (ssss))

Helen Caines


Are we in thermal/chemical equilibrium?

Compare particle ratios to experimental data

Qi : 1 for u and d, -1 for u and dsi : 1 for s, -1 for sgi : spin-isospin freedom

mi : particle mass

Tch : Chemical freeze-out

temperatureq : light-quark chemical potential

s : strangeness chemical potential

s : strangeness saturation factor

Particle density of each particle:Statistical Thermal Model

Assume: ♦ Ideal hadron resonance gas ♦ thermally and chemically equilibrated fireball at hadro-chemical freeze-out

Recipe:♦ GRAND CANONICAL ensemble to describe partition function density of particles of species i

♦ fixed by constraints: Volume V, ,

strangeness chemical potential S,

isospin♦ input: measured particle ratios♦ output: temperature T and baryo-chemical potential B

Helen Caines


Canonical vs Grand Canonical– Canonical (small system i.e. p-p):

Quantum Numbers conserved exactly.

Computations take into account energy to create companion to ensure conservation of strangeness.

Relative yields given by ratios of phase space volumes

Pn/Pn’ =n(E)/n’(E)

– Grand Canonical limit (large system i.e. central AA):

Quantum Numbers conserved on average via chemical potential Just account for creation of particle itself.

The rest of the system “picks up the slack”.

Not new idea pointed out by Hagedorn in 1960’s(and much discussed since)

Helen Caines


Comparison to data

Canonical ensemble

Au-Au √sNN = 200 GeVSTAR Preliminary

p-p √s = 200 GeVSTAR Preliminary

B 45 ± 10 MeV

S 22 ± 7 MeV

T 168 ± 6 MeV

s 0.92 ± 0.06

T 171 ± 9 MeV

s 0.53 ± 0.04

Helen Caines


Centrality and energy dependence

●, K,p●, K,p, ,●, K,p●, K,p, ,

Small Nch dependence of s

Chem. equilibrium !

Close to net-baryon free

Tch flat with centrality

Energy dependence of B

TLQCD~160-170MeV

and 62 GeVSTAR preliminary Au+Au at √sNN=200GeV

Helen Caines


Centrality dependence

STAR PreliminaryWe can describe p-p and Au-Au average ratios.

Can we detail the centrality evolution?

Look at the particle enhancements.

E(i) = YieldAA/Npart Yieldpp /2

Au-Au √sNN = 200 GeV

Transition described by E(i) behaviour

There is an enhancementE() > E()

Helen Caines


Strangeness phase space suppression - s

Canonical suppressionincreases with strangeness

decreases with volume

Canonical system – p-p Small system Lack of phase space available Strangeness suppressed

Grand Canonical system – central A-A

Large system Large phase space available Strangeness saturated

Helen Caines


Model description of centrality dependence

STAR Preliminary

K. Redlich

Correlation volume:

V= (ANN) ·V0

ANN = Npart/2 V0 = 4/3 ·R0

3

R0 = 1.1 fm proton radius/strong interactions

T = 170 MeVT = 165 MeV

Seems that T=170 MeV fits data best – but shape not correct


Helen Caines


Varying T and R

Calculation for most central Au-Au data

Correlation volume: V0 R0

3

R0 ~ proton radius strong interactions

Rapid increase in E(i) as T decreases

SPS data indicated R = 1.1 fm K. Redlich


Helen Caines


Npart dependence

STAR Preliminary

K. Redlich

Correlation volume:

V= (ANN) ·V0

ANN = Npart/2 V0 = 4/3 ·R0

3

R0 = 1.2 fm proton radius/strong interactions

T = 165 MeV = 1T = 165 MeV = 2/3T = 165 MeV = 1/3

Npart is NOT directly correlated to the strangeness volume.


Helen Caines


PHOBOS: Phys. Rev. C70, 021902(R) (2004)

More on flavour dependence of E(i)

PHOBOS:

measured E(ch)for 200 and 19.6 GeV

Enhancement for all particles?

Yes – not predicted by model

STAR Preliminary

s quark content determines E


Helen Caines


Moving from the bulk

ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

<Nbinary>/sinelp+p

p+p cross section

Compare Au+Au with p+p Collisions RAA

NuclearModification Factor:

R < 1 at small momentaR = 1 baseline expectation for hard processesR > 1 “Cronin” enhancements

(as in pA)R < 1: Suppression

A+A yield

Helen Caines


Rcp vs RAA

Effect increases as strange

content of baryon increases.

Canonical suppression in p+p

Rcp RAA

√sNN = 200 GeVSTAR Preliminary

√sNN = 200 GeVSTAR Preliminary

Helen Caines


Parton recombination at medium pT

• Parton pT distribution is

~exponential+power-law

•7 GeV particle via :

Fragmentation from high pT

Meson - 2 quarks at ~3.5 GeV

Baryon - 3 quarks at ~2.5 GeV

Recombination - more baryons than mesons at medium pT

Helen Caines


RCP - an energy scan√sNN=200 GeV

√sNN=62 GeV 0-5%

40-60%

0-5%

40-60%

NA57, PLB in print, nucl-ex/0507012

√sNN=17.3 GeV

First time differences between and B absorption?

Baryon meson splitting at all energies

Helen Caines


STAR Preliminary

NA57: G. Bruno, A. Dainese: nucl-ex/0511020

Baryon/meson splitting at SPS and RHIC is the

same

62 GeV Au+Au data also

follows the same trend

Recombination present in all systems?

The Rcp double ratio

Helen Caines


Conclusions

• Thermal models give good description of the data as function of energy and centrality.

• The enhancement of strangeness as a function of centrality CAN be described– scales with Npart

1/3 NOT Npart

• Non-strange particles are enhanced – NOT predicted by phase space models.

• The phase space effects of p-p extend into high pT regime.

• Baryon/meson splitting energy independent. ReCo at SPS.

Helen Caines


BACKUP

Helen Caines


Predictions from statistical model

Tpart

B

B

BeN

nBV

VnB

/

/

part

partT

Tpart

TT

N

Ne

eNee

Vn

S

BSB

/

/// )(

partT

partTT

Tpart

TT

Ne

Nee

eNee

Vn

B

SB

BSB

/2

//2

/// )(

Behavior as expected

Helen Caines


mT scaling

STAR Preliminaryp+p 200 GeV

No complete mT scaling

Au-Au

Radial flow prevents scaling at low mT

Seems to scale at higher mT

p-p

Appears to be scaling at low mT

Baryon/meson splitting at higher mT – Gluon jets?

Helen Caines


Gluon vs quark jets in p-p

Quark jets events display mass splitting

Gluon jets events display baryon/meson splitting

No absolute mT scaling – “data” scaled to match at mT~1 GeV/c

Way to explore quark vs gluon dominance

Helen Caines


Recombination and v2

Works for p, , K0s, ,

v2s ~ v2

u,d ~ 7%

The complicated observed flow pattern in v2(pT) for hadrons

is predicted to be simple at the quark level pT → pT /n

v2 → v2 / n ,

n = (2, 3) for (meson, baryon)

)2cos( )( 21 2

2

T

T

pvddp

Nd

Helen Caines


STAR preliminarySTAR preliminary

ReCo model and Correlations

R. Hwa, Z. Tan: nucl-th/0503060

The ratio of near side yields in central to peripheral collisions is around 3 at 1 GeV/c and decreases with increasing pT

assoc

This is in good qualitative agreement with ReCo model predictions though there are some differences to the model

(trigger pT, centrality)Long range dη correlations are visible in the STAR data and not taken into account in the plot. This is pT dependent and

may reduce any slope.

STAR preliminarySTAR preliminary

0-10%/40-80%

3 < pTtrigger < 6

Helen Caines


Recent ReCo Model Predictions

Premise:

Observables:

1)The ratio of Ω/Φ yields should rise linearly with pT

2) Any Ω or Φ di-hadron correlations are swamped by

the background and not observed

STAR Preliminary

STAR Preliminary

The production of Φ and Ω particles is almost exclusively from thermal s quarks even

out to 8 GeV/c

Being actively studied, but no results are available as yet

Helen Caines


Correlations: near side yields

STAR Preliminary

STAR Preliminary

No trigger particle

dependence in the near side yield/trigger in either d+Au

or Au+Au

d+Au Au+Au

STAR Preliminary

No definite trigger particle dependence vs centrality

butmeson triggers appear to be

systematically below baryon triggersReason for increase may be

due to longe range correlations in η

Helen Caines


Strange Correlations in Au+Au

• ΔΦ correlations per trigger particle

• 3 < pTtrigger < 3.5 GeV/c

• 1 < pTassoc < 2 GeV/c

• |η| < 1

Correlations corrected for TPC acceptance

and efficiency of associated particles

Near side

v2 is then subtracted to give final correlations

Helen Caines


RAA - A mocked upstring picture does well

Topor Pop et al. hep-ph/0505210

HIJING/BBar + KT ~ 1 GeVStrong Color Field (SCF) qualitatively describes RAA.

SCF - long range coherent fields

SCF behavior mimicked by doubling the effective string tension

SCF only produced in nucleus-nucleus collisions RAA≠ RCP

Are strong color fields the answer?

Helen Caines


RAA for central and peripheral data

Peripheral and central data both show an enhancement

Peripheral data is more enhanced – Cronin effect?



Helen Caines


Baryons/Mesons

The Λ/K0S ratio

exhibits a peak in the intermediate pT region.The peak high varies with centrality.

At higher pT the ratios for all centralities converge again.

nucl-ex/0601042

Magnitude and shape of ratio cannot be explained by flow alone.

Helen Caines


Particle identification

Approx. 10% of a central event

V0

K0

p

p

and by extension

K

Kink

K

a) dE/dx

b) RICH

c) Topology

K p d

e

Helen Caines


gluon vs quark jets

• Has been studied in e+e- collisions at higher energies

• Quark jets tend to fragment harder than gluon jets

• We can study this with identified strange hadrons in p+p collisions in STAR

Helen Caines


Helen Caines


• pT reach constrained by p+p data

• Some hint of splitting in the baryons - RAA ≠ RCP

• HIJING BB predicts such a splitting using Strong Colour Fields...

• See also the Corona effect in EPOS

Identified Particle RAA

(TOF)

PRC 72: 054901

Helen Caines


Strange particles at intermediate pT

The statistics from Run 4 allow us to go much higher in pT than previously and to study the intermediate pT

region in detail

ΛK0S

Helen Caines


Strange Di-hadron Correlations

• Observed suppression of single particle spectra compared to p+p and d+Au

• Disappearance of back-to-back jets

parton

hadrons

hadrons

parton

p, π, Λ, K, Λ

p, π, Λ, K, Λ

Charged Hadrons

•Baryon/meson puzzle at intermediate pT

•Particle production mechanisms

•quark vs gluon jets

Identified Hadrons

Coalescence/Recombinationor

Medium modified jets

Helen Caines


Multiplicity scaling with log(√s)

PHOBOS White Paper: Nucl. Phys. A 757, 28, nucl-ex/0410022

If I can describe dNch/das function of√s

Can we describe other observables in terms of dNch/dη ?

dNch/dη - strongly correlated to the entropy of the system!

Helen Caines


HBT and dNch/d

HBT radii ~linear as a function

Npart1/3

Even better in (dNch/d)1/3

power 1/3 gives approx. linear scale

nucl-ex/0505014 M.Lisa et al.

Scaling works across a large energy range

Helen Caines


First make a consistency check

Require the models to, in principle, be the same.

1. Only allow the least common multiple of parameters: T, q, s, s

2. Use Grand Canonical Ensemble.

3. Fix weak feed-down estimates to be the same (i.e. at 100% or 0%).

Helen Caines


The results

Ratio STAR Preliminary

p/p

p

1.01±0.02

0.96±0.03

0.77±0.04

0.15±0.02

0.082±0.009

0.054±0.006

0.041±0.005

(7.8±1) 10-3

(6.3±0.8) 10-3

(9.5±1) 10-4

1.01±0.08

after feed-down

increase s

decrease T

1 error

Not identical and feed-down really matters

Similar T and s

Significantly different errors.


Helen Caines


Centrality dependence

We can describe p-p and Au-Au average ratios.

Can we detail the centrality evolution?

Look at the particle enhancements.

E(i) = YieldAA/Npart Yieldpp /2

STAR Preliminary

Solid – STAR Au-Au √sNN = 200 GeV

Hollow - NA57 Pb-Pb √sNN = 17.3 GeV

Helen Caines


Ω : central collisions Motivation Chemistry Dynamics Summary

Tdec = 164 MeVTdec = 100 MeV

Ω- spectra, central

NNAu+Au, s = 200 GeVNNAu+Au, s = 62.4 GeV

• Data best reproduced with– Tdec ≈ 100 MeV

– Same as for π-, K-, p– Agreement holds for entire spectra!

• Same results at both energies!

P.F. Kolb and U. Heinz, nucl-th/0305084

• Tdec ≈ 164 MeV (decoupling at hadronization): not enough radial flow

pT = 2 GeV/c

Ideal Hydrodynamics

Helen Caines


Blast wave fits to data

(GeV

) 200 GeV

Strong centrality dependence on freeze

out parameters for light hadrons

Multi-strange hadrons freeze out earlier, with

a lower <βT>

Indicative of smaller cross-section for

interactions of multiply strange hadrons with

lighter species.

Is this a signature of partonic collectivity?

Helen Caines


What interactions can lead to equilibration in < 1 fm/c?Need to be REALLY strong

Microscopic picture

R. Baier, A.H. Mueller, D. Schiff, D. Son, Phys. Lett. B539, 46 (2002).MPC 1.6.0, D. Molnar, M. Gyulassy, Nucl. Phys. A 697 (2002).

Perturbative calculations of gluon scattering lead to long equilibration times (> 2.6 fm/c) and small v2.

v2

pT (GeV/c)

2-2 processes with pQCD = 3 mb

Clearly this is not the weakly coupled perturbative QGP we started looking for.

s(trong)QGP

Helen Caines


RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

1 km

v = 0.99995c

Au+Au @ sNN=200 GeV

Relativistic Heavy-Ion Collider (RHIC)

Helen Caines


Runs so far

Run Year Species √s [GeV ] Ldt

01 2000 Au+Au 130 1 b-1

02 2001/2 Au+Au 200 24 b-1 p+p 200 0.15 pb-1

03 2002/3 d+Au 200 2.74 nb-1 p+p 200 0.35 pb-1

04 2003/4 Au+Au 200 241 b-1 Au+Au 62 9 b-1

05 2004/5 Cu+Cu 200 3 nb-1 Cu+Cu 62 0.19 nb-1 Cu+Cu 22.5 2.7 b-1 p+p 200 3.8 pb-1

Helen Caines


A theoretical view of the collision

Tc – Critical temperature for transition to QGPTch– Chemical freeze-out (Tch Tc) : inelastic scattering stopsTfo – Kinetic freeze-out (Tfo Tch): elastic scattering stops

♦ Hadronic ratios.

♦Resonance production.

♦ p spectra.

♦ Partonic collectivity.

♦ High p measurements.

4

31 2

Helen Caines


Comparison between p-p and Au-Au

T 171 ± 9 MeV

s 0.53 ± 0.04

r 3.49 ± 0.97 fm

Canonical ensemble

T 168 ± 6 MeV

s

0.92 ± 0.06

r 15 ± 10 fm


p-p √s = 200 GeVSTAR Preliminary

Helen Caines


Resonances and survival probability

Chemical freeze-out

Kinetic freeze-out

measured

lost

K

K lost

K*

K*

K

K*

Kmeasured

♦ Initial yield established at chemical freeze-out

♦ Decays in fireball mean daughter tracks can rescatter destroying part of signal

♦ Rescattering also causes regeneration which partially compensates

♦ Two effects compete – Dominance depends on decay products and lifetime

time

Ratio to “stable” particle reveals information on behaviour and timescale

between chemical and kinetic freeze-out

K*

K

Helen Caines


P. Braun-Munzinger et.al.,PLB 518(2001) 41, priv. communication Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81. M. Bleicher and Horst Stöcker J. Phys.G30 (2004) 111.

Chemical to kinetic freeze-out

Finite time span from Tch to Tfo

If only rescattering K(892) most suppressed

Life-time [fm/c] :

Need rescattering and regeneration to “fix” the picture.

Helen Caines


Strong collective radial expansion

T

pure thermalsource

explosive source

T,

mT1/m

T d

N/d

mT light

heavy

mT = (pT2 + m2)½

Au+Au central , √s = 200 GeV

Good agreement with hydrodynamicprediction for soft EOS (QGP+HG)

Tdec = 165 MeVTdec = 100 MeV

• Different spectral shapes for particles of differing mass strong collective radial flow

Tfo~ 100 MeVT ~ 0.55 cNeeds “initial kick”

mT1/m

T d

N/d

mT

light

heavy

Model (plot) from P.F. Kolb and R. Rapp, Phys. Rev. C 67 (2003) 044903

Helen Caines


Anisotropic/Elliptic flow

Almond shape overlap region in coordinate space

Anisotropy in momentum space

Interactions/ Rescattering

dN/d ~ 1+2 v2(pT)cos(2) + …. =atan(py/px) v2 =cos2

v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane

Elliptic flow observable sensitive to early evolution of system

Mechanism is self-quenching

Large v2 is an indication of early thermalization

Time –M. Gehm, S. Granade, S. Hemmer, K, O’Hara, J. Thomas - Science 298 2179 (2002)

Helen Caines


Strong elliptic flow observed

Compatible with early equilibration

200 GeV Au+AuSTAR preliminary

v2(p

T)

pT (Gev/c)

0

0.1

0.2v2(K) > v2() > v2()

Hydrodynamical models with soft Equation-of-State describe data well for pT (< 2.5 GeV/c)

Although poor statistics even flows - low hadronic cross-section.

Evidence v2 built up in partonic phase

Helen Caines


Hydro: small mean free path,lots of interactions NOT plasma-like

The perfect fluidFirst time: hydrodynamics quantitatively describes heavy ion reactions at low pT.

Prefers a QGP EOS

Hydro without any viscosity.An ideal (perfect) fluid

Thermalization time t=0.6 fm/c and =20 GeV/fm3

Helen Caines


Moving away from the bulk ...

Helen Caines


Strangeness in p+p

•Large statistics data-set allows for the detailed analysis of data

Van Leeuwen , nucl-ex/0412023

NLO calculations show good

agreement with non-strange hadrons

STAR Preliminary

Agreement with strange hadrons is not as apparent,

better for AKK than for Vogelsang

Using Pythia (LO) requires changing

the K factor to match the data

EPOS has very good agreement with all particles, even Xi

Documents

Helen Caines Yale University Gordon Research Conference – New London, NH– June 2006 Collisions at RHIC are very strange Outline Bulk matter Equilibrium