ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 11

Collective Dynamics at RHICCollective Dynamics at RHIC

J. Fu, H. Huang, M. Kaneta, F. Liu, H.G. Ritter, K. Schweda, R. Snellings, Z. Xu, E. Yamamoto…

Nu Xu LBNL, Berkeley, USA

1) Introduction: QGP partonic collectivity

2) Some results from SPS and RHIC

3) Summary and outlook

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 22

IntroductionIntroduction

1) Initial Condition - baryon transfer - ET production - parton dof

2) System Evolves - parton/hadron expansion

3) Bulk Freeze-out - hadron dof - interactions stop

??

?

?

?

?

J/D

K*

,

K

p

d, HBT

vv22 saturates saturates

TT saturates saturates

Q2

time

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 33

Pressure, Flow, …Pressure, Flow, …

pdVdUd Thermodynamic identity

– entropy p – pressureU – energy V – volume= kBT, thermal energy per dof

In nuclear collisions, interactions among constituents and density distribution lead to: pressure gradient collective flow

number of degrees of freedom (dof) Equation of State (EOS) time integral – partonic + hadronic effects

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 44

Transverse flow observablesTransverse flow observables

As a function of particle mass:• Directed flow (v1) – early• Elliptic flow (v2) – early• Radial flow – integrated over whole evolution

Note:1) Effect of collectivity is additive – final effect is the sum of all processes as long as interactions are there. 2) No thermalization is needed – pressure gradient only depends on the density gradient and interactions.

1i

Ritttt

))ψcos(i(2v1dydpp

dN

2π

1

dyddpp

dN

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 55

Results from RHICResults from RHIC

1) At RHIC ~ constant vs. centrality2) At AGS, ratios changes factor ~100 / SPS factor ~ 2 variation

re-scatterings at hadronic stage reduced at RHIC

STAR: Phys. Rev. Lett. 86, 4778(01), 87, 262301(01), 89, 092301(02)

pΛ

pΛp,p

STAR preliminary

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 66

Proton flow at RHICProton flow at RHIC

1) <pt> increases with

centrality flow

2) RQMD describes

transverse motion well

hadronic re-scattering

3) It underestimates pbar

yield due to large

annihilation x-section

re-scattering at

earlier stage?

197197Au + Au + 197197Au at 130 GeV Au at 130 GeV STAR Preliminary

Fiducial yields

Total yields Systematic errors

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 77

Transverse momentum distributionTransverse momentum distributionSPS: GeVsNN 3.17

)/exp(

22

Tmf

masspm

T

TT

NA44, Phys. Rev. Lett. 78, 2080(97)

Dependence on the particle mass and the size of the colliding system collective flow !

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 88

T vs. mass plotT vs. mass plot (SPS)(SPS)

Interactions with hadronic gas:

Large x-section limit: pions, kaons, protons

Small x-section limit: , J/

sensitive to hadronization!

2 massTT thermalfo C

22ti

i

pm-exp

At SPS, the observed collective transverse flow, ~ 0.4c, develops mostly at the hadronic stage. and J/ do not flow!

H. van Hecke, H. Sorge, N. Xu, Phys. Rev. Lett. 81, 5764(98).

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 99

Beam energy systematicsBeam energy systematics

1) Smaller baryon chemical potential B = 45 MeV with Tch = 170 MeV

Approaching net-baryon free ! 2) Stronger transverse flow, T= 0.55(c)

More explosive expansion !

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 1010

vv22 for K for K00 and and

1) Integrated v2 increases with particle mass ;2) Hydro model results are consistent with data. ‘QGP’ EoS used in calculations! Does v2 signal partonic flow?

STAR Phys. Rev. Lett. 87, 182301(01) STAR, Phys. Rev. Lett. , accepted, (02)

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 1111

Transverse collective flowTransverse collective flow

Heavier mass particles show stronger collective flow effects !PHENIX: Phys. Rev. Lett. 88 242301(02) / STAR: Phys. Rev. C65, 041901(02) / STAR: Phys. Rev. Lett. 89, 092301(02)

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 1212

Slope parameters vs. massSlope parameters vs. mass

gluon

tii

n

pm

00

22

-exp

At high energy, high gluon density and strong interactions partonic flow

, D, J/ sensitive to partonic collectivity ?

??

At RHIC, the observed collective transverse flow, ~ 0.55c, sum of partonic and hadronic interactions ! and J/ should flow!

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 1313

Partonic Flow at RHIC?Partonic Flow at RHIC?

??

We need: 1) Non-zero values of v2 for 2) Increase of T for , D, J/ …

YES

NO

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 1414

SummarySummary

1) SPS: most of the collective flow develops at later hadronic stage2) RHIC: Copious scattering needed,Copious scattering needed, Not at the later hadronic stage,Not at the later hadronic stage, Evidence of early patonic flow?! Evidence of early patonic flow?!

3) To ‘see’ the partonic flow directly, spectra and v2 for all hadrons, especially,

s s D J/ D J/ ... ...

ISMD XXXII, September 7–14, 2002 Nu XuNu Xu 1515

OutlookOutlook

Discover partonic collectivity – ‘QGP’ New Form of Matter !New Form of Matter !Diagnose bulk properties of ‘QGP’

Important: Scan collision geometry b Scan collision size A Scan collision energy E