Sergey Panitkin

Pion HBT in Cu+Cu Collisions at RHIC

Sergey Panitkin

Brookhaven National Lab

STAR Collaboration

Sergey Panitkin

Outline

Introduction and motivation Experimental details Analysis results Comparison to AuAu @ 200 GeV Comparison to theoretical predictions Summary

Sergey Panitkin

Identical meson correlations

Kt~x~KR

Kx~KR

Kt~x~KR

2llong

2l

2side

2s

2out

2o

xxx~

)K,x(Sxd

)x(f)K,x(Sxdf

4

4

Decompose q into components:qLong : in beam directionqOut : in direction of transverse momentum KT

qSide : qLong & qOut

222222

1),,( llssoo RqRqRqlso eqqqC

Radii are related to source variances:

221

21

ppk

ppq

In Longitudinally Co-Moving System (LCMS) l =0

Sensitive to emission time

Sensitive to transverse extent

Sensitive to longitudinal extent

Sergey Panitkin

Femtoscopic signature of QGP

3D 1-fluid Hydrodynamics

Rischke & Gyulassy, NPA 608, 479 (1996)

withtransition

“”

Long-standing favorite signature of QGP:

• Lattice QCD -> Speed of sound goes to zero (pressure drop) at phase transition

• increase in , ROUT/RSIDE due to deconfinement confinement transition

• hoped-for “turn on” as QGP threshold is reached (“softest point”)

G. Boyd et al., , Nucl.Phys. B469 (1996) 419

Sergey Panitkin

•AuAu (PbPb)•Y~0•<Kt>~170 MeV•Central ~10%

Energy dependence of pion HBT

RHIC HBT Puzzle #1Smooth energy dependence

Where is the softest point ?

Lower energies?Lighter systems?

Sergey Panitkin

STAR 200 GeV Cu+Cu Min. bias statistics

• Total: 64.47 Mevts of Min-bias• Min bias Trigger was operational for 52 days.

Ave/day ~ 1.24 Mevts

~5M events used for this analysis

Sergey Panitkin

Centrality selection in Cu+Cu Collisions

Reference multiplicity in TPC |y|<0.5

1 2 3 4 5 6

10%

20%

30%

40%

50%

60%

Sergey Panitkin

Centrality dependence of the Kt dependence

STAR preliminary

Cu+Cu @ 200 GeV, positive pions

Radii decrease for less central eventsRadii decrease with Kt (consistent with flow)Lambda parameter grows with Kt

Ro

Rs Rl

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Comparison to Au+Au at 200 GeV

Most central:AuAu 0 - 5%CuCu 0 – 10%

STAR preliminary

Sure, Cu is smaller than Au !

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Expansion in Heavy Ion Collisions

•x2 expansion in AuAu

•Cu bridges dAu and AuAu

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Multiplicity scaling of pion radii at RHIC

•CuCu bridges multiplicity rangebetween dAu and AuAu

•Radii scale with multiplicity fromperipheral dAu to central AuAu

•Scaling holds with Kt

•62 GeV AuAu data follow the same systematics

STAR preliminary

Sergey Panitkin

Cramer-Miller predictions for Cu+Cu

nucl-th/0507004 See talk by John Cramer

Scaled AuAu space-time parameters by (63/197)1/3 works?

KtKt

First prediction of HBTRadii for Cu+Cu

STAR preliminary

Sergey Panitkin

Summary

First HBT measurements in Cu+Cu collisions at RHIC at 200 GeV

Preliminary pion HBT radii in Cu+Cu show clear centrality and Kt dependence, similar to Au+Au

Expansion in heavy ion collisions

Multiplicity scaling of pion (Nch1/3 ) radii is observed,

similar lower (AGS, SPS ) energies

Consistent with no change in dynamics between CuCu and AuAu