1

2-particle correlation at RHIC

Fabrice Retière, LBNL

for the STAR collaboration

2

Outlines

Hydro at RHIC Rather successful for spectra and elliptic flow

But, cannot describe pion HBT

A blast wave model?Very strong flow

Short emission duration

More constraints : new 2-particle correlations from STAR

Pion HBT with respect to the reaction plane

Kaon HBT

Kaon – pion correlations

3

R

t

RsideRout

Kt = pair Pt

Blast wave featuresInterplay between flow and temperature

Correlation position - momentum

Short emission duration

Hydro lower limit

+

-

Rou

t (fm

) 6

0.2 0.3 Pt (GeV/c)

5

4

6

5

4

1

0.9

0.8

Model :R = 13.5 fm, = 1.5 fm/cT = 110 MeV, <t> = 0.52c

0.1

Rsi

de (

fm)

Rou

t/R

side

Data, Phys.Rev.Lett. 87, 082301 (2001)

Pion HBT explained in a blast wave scenario

4

Other blast wave model successSpectra and elliptic flow

-

K-

p

1/m

T d

N/d

mT

(a

.u.)

mT - m [GeV/c2]

Additional features for v2Momentum and position anisotropy

STAR preliminary

Submitted to PRL

Masashi Kaneta

A. Poskanzer, R. Snellings, S.Voloshin

5

HBT and Elliptic flow

OscillationsFrom flow

From space asymmetry

Rside2 (fm2)without flowOnly space asymmetry

(deg)

=0 degreeRout largeRside small

=90 degreeRout smallRside large

In plane example

6

HBT and Elliptic flowResult from STAR

Clear in-plane oscillation

Blast wave fitR=10 fm, T=110 MeV, <t> = 0.52c

Consistent with other measurements

Favor a scenario with an anisotropy both in space and momentum

STAR preliminary

Randy Wells, Mike Lisa

7

More constraints to the blast wave model : mass dependence

Kp

mT (GeV/c2)0.0. 0.2 0.4 0.6 0.8 1. 1.2

0.4

(a.u.)Blast wave

0.5

0.6

NA44 @ SPSPRL 87 (2001) 112301

8

Mass scaling?Kaon HBT

STAR preliminary

Rinv = 4.5 ± 0.3 fm (stat)

Coming soon 2D/3D HBT

Needed for comparison to the blast wave modelQinv (GeV)

C(Q

inv)

Sergei Panitkin

9

Kaon – pion correlation

Static sphere : R= 7 fm ± 2 fm (syst+stat)

Blast wave T = 110 MeV (fixed)

<t> = 0.52c (fixed)

R = 13 fm ± 4 fm (syst+stat)

Consistent with other measurements

STAR preliminary

10

Probing the space-time emission asymmetry

Kinematics selection

Catching up Large interaction time Large correlation

Moving away Small interaction time Small correlation

Ratio Sensitive to the space-time asymmetry

11

Space-time asymmetry

Evidence of a space – time asymmetry

-K ~ 4fm/c ± 2 fm/c, static sphere

Consistent with “default” blast wave calculation

Kaon <pt> = 0.42 GeV/c

Pion <pt> = 0.12 GeV/c

STAR preliminary

12

Conclusions and outlook

New measurements from STAR :

Pion HBT with respect to reaction plane

Kaon HBT

Kaon-pion CF

Qualitative agreement with a blast wave scenario

But, so far, cannot be achieved by any hydro or microscopic model

NextPion HBT

@ 200 GeV (and others)

More statistics for reaction plane dependence

Different mass3D K+,K- , proton, K0

s,

More non-identicalPion-proton

Proton-@ 200GeV

Pion-- @ 200GeV?

13

First sign of emission asymmetry @ RHIC

14

Strong flow and short emission duration at RHIC

Consistent with Spectra

Elliptic flow

Pion HBT

Pion HBT wrt reaction plane

Pion – kaon correlation function

Question for theoristsHow to get there?

Kaon <pt> = 0.42 GeV/c

Pion <pt> = 0.12 GeV/c

15

Back up

16

Kaon Hbt

7 MeV/c bins

Positive Kaons, Mult 3 (~11% Central), Pt 150-400 MeV/c, |y|<0.3

Qinv (GeV/c)

17

Kaon Hbt and coulomb

18

Chi2 contourT t

h [G

eV]

s [c]

T th [

GeV

]

s [c]

19

error contour fromelliptic flow data

color: 2 levelsfrom HBT data

20

Equations

)())((1),( )cos()( rRerKpxf dr

))(cosh(*)( rT

Mr T

))(sinh()( rT

Pr T

n

R

rr )()(

00