Sergey Panitkin

Sergey Panitkin

RHIC/AGS User Meeting

2006

Energy dependence of the Bose-Einstein Correlations

Sergey Panitkin

Outline

Introduction

Energy dependence of pion correlations

Azimuthally sensitive pion HBT

Summary

Sergey Panitkin

Two-particle Correlations

Single particle spectrum is sensitive to momentum distribution only

Relative momentum distribution of particle pairs is sensitive to space-time information

Basis for Identical and Non-identical particle femtoscopy

),(4 pp

xSdxddNE

),(|),(|)/)(/(

/)( 2

2111

2122 qrqrr

pppp

q SdddNddN

dddNC

Source functionFSI

System evolution encoded in S(r,q)

Sergey Panitkin

qout

qside

qlong

Hanbury Brown-Twiss interferometry

Rsi

de

R long

Rout

x1

x2

12 ppq

p1

p2

q

12 pp2

1k

Pratt-Bertsch parameterization

HBT: Quantum interference between identical particles

pairsevent mixed

pairsevent real

)(P)(P

),(P),(

21

2121

pp

ppppC

2long

2long

2side

2side

2out

2out)(1),(

RqRqRqekkqC

q (GeV/c)q (GeV/c)

C (

q)C

(q)

11

22R

1~

– Final-state effects (Coulomb, strong) also can cause correlations, need to be accounted for

Gaussian model (3-d):

Sergey Panitkin

HBT for Gaussian sources

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

Mt dependence

Charged pions, AuAu (PbPb) most central

Mt dependence is attributed to collective flow

Sergey Panitkin

Femtoscopic signature of QGP

3D 1-fluid Hydrodynamics

Rischke & Gyulassy, NPA 608, 479 (1996)

withtransition

“”

Long-standing 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

Compilation of world BP 3D -HBT parameters as a function of s

• ~10% Central AuAu(PbPb) events

• y ~ 0

• kT 0.17 GeV/c

no significant rise in spatio-temporal size of the emitting source

STAR Preliminary

The HBT Excitation function circa 2001

QM 2001

Sergey Panitkin

Energy systematics 2006

•Many new measurements since 2001

•Same conclusions

Sergey Panitkin

<ßr> (RHIC) = 0.55 ± 0.1 cTKFO (RHIC) = 100 ± 10 MeV

• Rapid change in freeze-out temperature and flow velocity between 2-20GeV

• Explosive Transverse Expansion at RHIC High Pressure

•Almost constant freeze-out temperature above 20 GeV

Tth

[GeV

]< r

> [

c]

STA

R

Kinetic freezeout from AGS->RHIC

T. Nayak

Blast wave fits to spectra

Sergey Panitkin

Freeze-out volume vs. beam energy

• non-monotonic behaviour

• minimum between AGS and SPS

•Why there is a drop at AGS ?

√s(GeV)

<kt> ~ 0.16 GeV/c

CERES Phys. Rev. Lett. 90 (2003) 022301

H. Appelshauser

Freeze-out volume estimate: 2sidelong

3

f RR2V

•Not a simple concept for expanding sources with continuous emission•Because of flow the best “total volume” estimate is at low Kt•Ad hoc formula

Sergey Panitkin

????

Freeze-out volume

Freeze-out volume estimate: 2sidelong

3

f RR2V

0.15 < kt < 0.25 GeV/c

<Npart>

CERES Phys. Rev. Lett. 90 (2003) 022301 partf NV

Centrality dependence:

since

partch NN

.constf

only at given beam energy!!

2sidelong

3

f RR2V

Sergey Panitkin

Particle multiplicity vs. beam energy

CERES Phys. Rev. Lett. 90 (2003) 022301

• particle number increases monotonically freeze-out at constant density excluded

• chemical composition changes

• cross sections are very different try mean free path:

√s(GeV)

1

Sergey Panitkin

Mean free path

N

V1 f

ff

in a composed medium:

... NNN NN

mb mb, 1372N

CERES Phys. Rev. Lett. 90 (2003) 022301

√s(GeV)

also Nσ shows non-monotonic behaviour dominated by baryons at low energy and mesons at high energy

Sergey Panitkin

Universal pion freeze-out

N

V1 f

ff CERES Phys. Rev. Lett. 90 (2003) 022301

√s(GeV)

Nσ follows Vf

data are consistent with constant mean free path at freeze-out

fm 1f

independent of beam energy and centrality

Sergey Panitkin

Universal freeze-out II

universal pion freeze-out:

independent of beam energy and system size

in A-A: f << R

why no dependence on beam energy and system size? why so small?

fm 1f

sqrt(sNN) (GeV) f

(fm

)

NN

V

N

V1

NN

fff

..implies f.o. at constant density (R~(dNch/d)1/3) if particle ratios are constant!

H. Appelshauser

Sergey Panitkin

What is “true” scaling variable?

STAR Preliminary

Nch seems to be better

Sergey Panitkin

Multiplicity scaling of radii

STAR DATASTAR DATA (pp,dAu,CuCu,AuAu@62GeV - prelim.)

“Universal radii scaling”as a concequence of volume scaling

For different systems and energies at RHIC physics does not change!?

Multiplicity scaling seems to work at all measured Kt

Sergey Panitkin

HBT relative to reaction plane HBT()

• “Standard” HBT provides direct access to space-time (size) information about source, "HBT radii"

• Additionally, HBT() provides direct access to shape and orientation of source

• Source shape at freeze-out evolution of system"How much of initial spatial deformation still exists at freeze-out?"

later hadronic stage?

bx

beam into screen

Heinz & Kolb, Nucl.Phys. A702 (2002) 269-280

collective expansion of system

Sergey Panitkin

Elliptic geometry leads to oscillations of the radii

– For example Rside

b

Rsi

de2

(fm

2 )

Out-of-plane In-planeCircular

(degree)out-of-planeextended source

p=0°

p=90°

Rside (large)Reactionplane

Rside (small)

Naïve view with no flow

HBT with respect to reaction plane

Heinz, Hummel, Lisa, Wiedemann PRC 044903 (2002)

Sergey Panitkin

Predictions from hydro

• Hydrodynamics: initial out-of-plane anisotropy may become in-plane later hadronic stage?

in-plane-extended

out-of-plane-extended

Teaney, Lauret, & Shuryak, nucl-th/0110037Heinz & Kolb, hep-ph/0111075

kT dependence

Sergey Panitkin

Centrality Dependence of HBT()

12 -bin analysis (kT integrated)

15° bins, 72 CF's total 12 bins × 3 centrality bins × 2 pion signs

0.15 < kT < 0.65

Oscillations exist in transverse radii for all bins

Amplitudes weakest for 0-10%

• Lines represent fits to allowed oscillations:

out, side, long go as cos(2)out-side goes as sin(2)

STAR

Sergey Panitkin

Estimate of initial vs F.O. source shape

2x

2y

2x

2y

RR

RR

20,S

22,S

FO R

R2

• estimate INIT from Glauber

• from asHBT:

FO =

INIT

FO < INIT → dynamic expansion

FO > 1 → source always OOP-extended

• constraint on evolution time

RHIC1[Kolb & Heinz]

•Out of plane extended source •Short life time

Sergey Panitkin

• AGS: E895, RHIC: STAR• does it make sense? Is it related

to bulk dynamics? YES

sNN (GeV)

(approximately same centrality)

AGS: FO init

RHIC: FO < init

Exitation function

•AGS: E895, RHIC: STAR

•~200 GeV Gap in measurements

Sergey Panitkin

Summary

HBT is a valuable tool for studies of space-time structure of systems created in heavy ion collisions

Important additional constraint for spectra and v2 measurements Large systematic datasets are already collected from AGS, SPS and

RHIC Non-trivial energy dependence of HBT radii is observed

– No predicted signatures of 1st order phase transition are not (yet?) observed

– Non monotonic behaviour (dip) around 10 GeV – “CERES hypothesis” is tempting: Universal mean free path at f.o.?– Similar dynamics, hence chemistry drives freeze-out– Multiplicity scaling at SPS and RHIC

Azimuthally sensitive HBT provides additional unique information about reaction dynamics

Detailed measurements at RHIC (and AGS), no measurements at SPS– Out of plain extended sources observed, imply short (~10 fm)

source lifetime More measurements are needed Lower energy measurements around 10-20 GeV will be very interesting