Helen CainesYale University

1st Meeting of the Group on Hadronic Physics , Fermi Lab. – Oct. 2004

Bulk matter properties in RHIC collisions

Helen Caines

GHPM – Oct. 2004 2

Outline

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.

♦ pT spectra.

31 2

Helen Caines

GHPM – Oct. 2004 3

RHIC detectors designed for PID

So far the RHIC experiments have published identified So far the RHIC experiments have published identified particle spectra for:particle spectra for:

, , , K, K, K, K00ss, p, d, , p, d, , , ±

00, , , , , , , K, K*0*0(892), (892), *(1385), *(1385), *(1520)

DD00, D, D±, J/, J/’s’s (+ anti-particles)(+ anti-particles) …

V0 decay vertices

Ks + + -

p + -

p + +

- + -

+ + +

+ K -

Au+Au

40% to 80%

0.2 pT 0.9 GeV/c

0

f0

K0S

K*0

STAR Preliminary

dE/dx in TPC

Time of Flight (ToF)

Electron ID viap/E in EMC

Resonances in invariant mass spectra

Helen Caines

GHPM – Oct. 2004 4

A theoretical view of the collision

1

Chemical freezeout (Tch Tc) : inelastic scattering stops

Helen Caines

GHPM – Oct. 2004 5

What can Kaons tell us?

Kaons carry large percentage of strangeness content.

K- = us

K+ = su

Ratio tells about baryon

transport even though not a baryon.

Changing rapidity slice changes chemistry

Helen Caines

GHPM – Oct. 2004 6

Models to evaluate Tch and B

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

Tch : Chemical freeze-out

temperatureq : light-quark chemical potential

s : strangeness chemical potential

s : strangeness saturation factor

Particle density of each particle:Statistical Thermal ModelF. Becattini; P. Braun-Munzinger, J. Stachel, D. MagestroJ.Rafelski PLB(1991)333; J.Sollfrank et al. PRC59(1999)1637

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

GHPM – Oct. 2004 7

Centrality and Energy Dependence

●, K,p●, K,p, ,

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

TTLQCDLQCD~160-170MeV~160-170MeVTTLQCDLQCD~160-170MeV~160-170MeV

●, K,p●, K,p, ,

Energy dependence but small NEnergy dependence but small Nch ch dependence… dependence…

Close to chem. equilibrium !

Close to net-baryon free

Tch flat with centrality

Helen Caines

GHPM – Oct. 2004 8

Rapidity Dependence

Fit resultsMeanUpper/Lower error

• Tch, s

– Small sensitivity to y– Close to strangeness equilibration in

central collisions over y=0-3 (ybeam=6)

• q, s – Reflect baryon density with yBRAHMS Au+Au 200 GeV

Helen Caines

GHPM – Oct. 2004 9

(In)dependence of mid-rapidity yields

T, µB, and V can all vary with energy, but in such a way as to ensure yields stay ~constant

Preliminary

Preliminary

Preliminary

Helen Caines

GHPM – Oct. 2004 10

200 GeV Au+Au

Results of Fit

Strangeness Enhancement

Resonance Suppression

Au+Au only stable particle ratios well described

STAR Preliminary

200 GeV p+p

p+p particle ratios well described

Helen Caines

GHPM – Oct. 2004 11

How does volume affect production?

When reach grand canonical limit strangeness will

saturate.

– 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

GHPM – Oct. 2004 12

How can we observe this

♦ Canonical suppression increases with decreasing energy

♦ Canonical suppression increases with increasing strangeness

σ(Npart) / Npart = ε σ(pp) ε > 1 Enhancement!

Helen Caines

GHPM – Oct. 2004 13

SPS at √s= 17.3 & 8.8 GeV

C to GC predicts a factor 4 - 5 larger - enhancement at √sNN =8.8 GeV than at 17.3 GeVYields don’t have time to reach limit – hadronic system?

Temperature assumed is incorrect?

NA57 (D. Elia QM2004)

Helen Caines

GHPM – Oct. 2004 14

But does it over saturate or ONLY just reach saturation?

And then at RHIC (200 GeV)...

not flat any more!

,K,p

,K,p,

STAR Preliminary

Au-Au √s=200 GeV

Helen Caines

GHPM – Oct. 2004 15

Rcp of strange particlesR

cpBaryons and mesons are different

Helen Caines

GHPM – Oct. 2004 16

RAA of strange particles

Baryons with s quarks scale differently to non-strange.

h-

Phase space suppression in p+p vs jet suppression in Au+Au.

Helen Caines

GHPM – Oct. 2004 17

Is there a scaling?

The more strangeness you add the less it scales with Npart.

Npart scaling

Normalized to unity for 0-5% data

Helen Caines

GHPM – Oct. 2004 18

Is there a scaling?

The larger strangeness content scales better with Nbin.

Still not perfect.

Normalized to unity for 0-5% data

Nbin scaling

The more strangeness you add the less it scales with Npart.

Helen Caines

GHPM – Oct. 2004 19

s quarks have different scaling? How about scaling according

to quark content?

u, d – scale with Npart

– already observed.

s – scale with Nbin

– appears better for strange

particles.K0

s – 1/2*Npart + 1/2*Nbin

p – Npart

– 2/3*Npart + 1/3*Nbin

– 1/3*Npart + 2/3*Nbin

– Nbin

– Nbin

Pretty good!

Does strangeness “see” a different

correlation volume?– Npart

Helen Caines

GHPM – Oct. 2004 20

A theoretical view of the collision

Chemical freezeout (Tch ) ~ 170 MeVTime between Tch and Tfo

2

Helen Caines

GHPM – Oct. 2004 21

Resonance 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

GHPM – Oct. 2004 22

Resonance ratiosThermal model [1]: T = 177 MeV

B = 29 MeV

UrQMD [2]

*rescatt. > regen.* rescatt. > regen.rescatt. < regen.* rescatt. < regen.

[1] P. Braun-Munzinger et.al., PLB 518(2001) 41 D.Magestro, private communication[2] Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81-87. M. Bleicher, private communication

Need >4fm between Tch and Tfo

/

TT chfoStable

Resonance

Stable

Resonance te

Small centrality dependence: little difference in lifetime!

Helen Caines

GHPM – Oct. 2004 23

A theoretical view of the collision

31

Chemical freezeout (Tch ) ~ 170 MeVTime between Tch and Tfo 4fmKinetic freeze-out (Tfo Tch): elastic scattering stops

2

Helen Caines

GHPM – Oct. 2004 24

Shape of the mT spectrum depends on particle massTwo Parameters: Tfo and

Fit range : mT – mass < 1 GeV/c2

Hydro-dynamical model

Tfo ~110 MeV, < > = 0.8 c

tanh 1 r

R

s

E.Schnedermann et al, PRC48 (1993) 2462

dn

mT dmT r dr mT K1

mT coshT

0

R

I0pT sinh

T

r =s (r/R)n

PHENIX

Au-Au 200 GeV

Lattice QCD: Tc = 17010 MeV

Tch

STAR Preliminary

Helen Caines

GHPM – Oct. 2004 25

♦ , K, p: Common thermal freeze-out at Tfo ~ 90 MeV

<> ~ 0.60 c

♦ : Shows different thermal freeze-out behavior:

Tfo ~ 170 MeV

<> ~ 0.45 c

Multi-strange Kinetic Freeze-out

Tdec = 100 MeV

Kolb and Rapp,PRC 67 (2003)

044903.

Hydro does not need different T for multi-strange Freeze-out T different – Is blastwave realistic?

Are re-interactions till freeze-out realistic either?

Blastwave parameterization

Higher temperatureLower transverse flowProbe earlier stage of collision?

Helen Caines

GHPM – Oct. 2004 26

p+p is not trivial

Helen Caines

GHPM – Oct. 2004 27

pT spectra vs multiplicity

1) Re-bin and Divide by min.bias2) Scale by:<NMB>/ <Nk>

high mult. spectra are more enhanced at high pT then K0

s

→ More contribution of Minijets ??

Helen Caines

GHPM – Oct. 2004 28

Summary

Appear to have strangeness saturation at most central top

RHIC energies but not before (s = 1).

Do s quarks “see“ a different correlation volume to light quarks?There is a rescattering between Tch and Tfo.

There is strong radial flow in Au-Au system.

Seems that and freeze-out differently.62.4 GeV rather similiar to 200 GeV

Our simple thermal pictures are only approximately correct.

The devil is in the details but we have the data to figure it all out.

Helen Caines

GHPM – Oct. 2004 29

Backup from here

Helen Caines

GHPM – Oct. 2004 30

What happens to other particles?

– Npart scaling

p – slight increase

phase space suppression

of baryons?

K0s – only small phase space

suppression of strange

mesons?

Not flat with centrality

What about the Containss and s quark, so not strangeshould show no volume dependence

factor 2 increase relative to p-p

Helen Caines

GHPM – Oct. 2004 31

from BaBar

Helen Caines

GHPM – Oct. 2004 32

Scale: (Nud/Nq)*Npart + (Ns/Nq)*Nbin Scale: (Nud/Nq)*0.5*Npart + (Ns/Nq)*Nbin

Helen Caines

GHPM – Oct. 2004 33

C: N ~ V2 (V 0)

GC: N ~ V (V )

Assume V ~ Npart

Pions/Apart constant

grand-canonical!

Kaons/Apart rising

canonical!

SIS energies

KaoS M. Mang et al.

J. Cleymans, H. Oeschler, K. Redlich, PRC 59 (1999)

Helen Caines

GHPM – Oct. 2004 34

Seems OK at SPS too

Again not bad

except for peripheral bin

- errors large.

Normalized to unity for 0-5% data

Helen Caines

GHPM – Oct. 2004 35

Thermal model reproduced dataD

ata

– F

it (s

)

R

atio

Do resonances destroy

the hypothesis?

Created a Large System in Local Chemical Equilibrium

Used in fit

Helen Caines

GHPM – Oct. 2004 36

Constraining the parameters

Helen Caines

GHPM – Oct. 2004 37

How about at SPS?Again :

The more strangeness the less the particle scales with Npart.

Nbin scaling not correct either.

u,d vs s quark scaling,

not bad except for most peripheral bin - errors large.Npart scaling

Normalized to unity for 0-5% dataNbin scaling

Helen Caines

GHPM – Oct. 2004 38

RAA of strange particles

K±, K0s, and h- all scale similarlyp, , show hierarchy.

Phase space suppression in p-p fighting jet suppression in Au-Au.

h-

Helen Caines

GHPM – Oct. 2004 39

Flow Effect on Spectra

PHENIX, STAR Preliminary200 GeV

Flow increases as centrality increases

p

Helen Caines

GHPM – Oct. 2004 40

Baryon transport to mid-rapidity Clear systematic trend with collision energy

B - all from pair production B - pair production + transported from ybeamto y=0

B/B ratio =1

- Transparent collisionB/B ratio ~ 0

- Full stopping, little pair

production

♦ ~2/3 of baryons from pair production♦ First time pair production dominates♦ Still some baryons from beam

Preliminary

Helen Caines

GHPM – Oct. 2004 41

p-p

Collective motion in Au-Audata / power law

Au-Au

not absolutemT scaling...

but if you rescale

not in Au-Au

data