Sergey Panitkin

Current Status of the RHIC HBT Puzzle

Sergey PanitkinBrookhaven National Lab

La Thuile, March 18, 2005

Sergey Panitkin

Who cares about the soft sector?

99.5%

• Well-justified excitement about high-pT physics

• But recall that we want to create/study a new type of matter (= bulk system)

• large-scale (soft?) deconfinement• Collective properties (T,p, flow?)

• Jets/ect are probes of this system

• Crucial to understand bulk properties and dynamics in their own right

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Collective behavior at RHIC

P. Kolb, J. Sollfrank, U. Heinz

Heinz & Kolb, hep-th/0204061

• Hydrodynamics seems to reproduce p-space aspects (spectra and elliptical flow) of particle emission up to pT~2GeV/c

Bulk system?!Note: Hydro provides complete space-time evolution. Can be tested!

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Two-particle Correlations

Single particle spectrum is sensitive to momentum distribution only

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

Intensity interferometry, HBT technique, etc….

),(4 pp

xSdxddNE

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

/)( 2

2111

2122 qrqrr

pppp

q SdddNddN

dddNC

Source functionFSI

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Two particle Interferometry: Idealized case

y

X

1

2

Source

24

2xiq4

21)K,x(Sxd

e)K,x(Sxd1)p,p(C

21 ppq 2121 ppK

emission function

For non-interacting identical bosons:

C (Q

inv)

Qinv (GeV/c)

1

2

0.05 0.10

Width ~ 1/R

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Correlation functions for different colliding systems

C2(

Qin

v)

Qinv (GeV/c)

STAR preliminary p+pR ~ 1 fm

d+AuR ~ 2 fm

Au+AuR ~ 6 fm

Correlations have more informationOne can use more sophisticated analysis to extract it

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beam direction

p1 p2

Q T

Q

Q L

beam direction

p2p1

Q T

Q S

Q O

“Standard” Pratt-Bertsch coordinate system

)T2

PT1

P(2

1T

K

2long

2long

2side

2side

2out

2out)(1),(

RqRqRqekkqC

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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

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In Search of the QGP. Naïve expectations

QGP has more degrees of freedom than pion gas

Entropy should be conservedduring fireball evolution

Hence: Look in hadronic phasefor signs of: Large size, Large lifetime, Expansion……

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In Search of the QGP. Expectations.

“Energy density”

•One step further:•Hydro calculation of Rischke & Gyulassy expects Rout/Rside ~ 2->4 @ Kt = 350 MeV.•Looking for a “soft spot”

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Excitation function of the HBT parameters

• ~10% Central AuAu(PbPb) events

• y ~ 0

• kT 0.17 GeV/c

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

Ro/Rs ~ 1

Some rise in Rlong

Note ~100 GeV gap betweenSPS and RHIC

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RHIC Energy Scan

•Measurements at 200, 130, 62 GeV

•No significant change with energy

•Ro/Rs ~1

PHOBOS nucl-ex/0409001

Where are signs of phase transition?!

Is HBT sensitive to geometry at all?!

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More Experimental Systematics

STAR PRL 93:12301 (2004)PHENIX nucl-ex/0401003

Clear sensitivity to source geometry !

b≠0

Centrality dependence asHBT

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Source expansion at RHIC

initi

al =

final

22

22

xy

xy

RR

RR

Rx

Ry

STAR preliminary

STAR Collaboration, nucl-ex/0312009

Expansion at low Pt Change in eccentricity of the source

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Model Comparison (the puzzle)

Subset of models shown

Broad range of physics scenarios explored

Good description of p-space

Poor description of HBT data

the puzzle

Does Rout/Rside of unity imply no long-lived mixed phase?

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x-tx-t Correlation of Source Function Correlation of Source Function

Why hydro doesn’t work? positive!

x

t

Negative x-t correlation

Positive? Negative?

Typical source functionfrom hydro with Bjorken flow

x

t

Positive x-t correlation

Hubble like flow?Buda-Lund, AMPT

Rout~Rside may require positive x-t corr.

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BudaLund fits to 130 GeV data

PRC54 (1996) 1390, NPA 590 (1995) 465

Parameterization, not a model !

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Conclusions

Rich set of experimental HBT results exists at RHIC Large number of models has been developed to explain RHIC physics Good description of momentum space observables Evidence that matter at RHIC exhibits collective bulk properties Most models still can not reproduce simultaneously experimental

observables at low Pt: v2, spectra, correlations, dN/dy, etc We are gaining better understanding of model failures Bjorken longitudinal boost-invariance assumption seems to be one of

the sources of discrepancies (at least for Hydrodynamical models) More detailed correlation measurements will be available soon: non-

identical correlations, HBT Pt>1 GeV/c, Kaons, protons, etc Stay tuned!

Sergey Panitkin

The END

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Back Up slides

Sergey Panitkin

Does HBT in rhic make sense?

YES… Size [R(Npart

1/3)] Shape [R( )] Dynamic structure [R(mT)]

… and NO? Model disagreement

[transport]? Too-short timescales [BW]

? Inconsistent dynamical picture

? No large rise in RO, RL [general]

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BL-H sourceparameters

BudaLundv2.0

BudaLundv2.0 Hubble+T

T0 [MeV] 182 19 160 15<ut> 1.16 0.09 fixed RG /0

RG [fm] 9.2 0.6 10.0 0.5

0 [fm/c] 7.3 0.6 7.9 0.4 [fm/c] 0.0 0.5 0.2 0.4 2.36 0.04 2.38 0.05Tsurf [MeV] 92 5 89 4Teva [MeV] 110 14 114 15

0- [MeV] 78 15 76 10

0K- [MeV] 134 30 148 16

0p- [MeV] 382 59 411 23

0+ [MeV] 65 12 66 8

0K+ [MeV] 162 30 173 15

0p [MeV] 446 58 467 22

/NDF 213./180 =1.19 214/181 =1.18

CL 4.5 % 4.5 %

Buda-Lund fits to 130 GeV data

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Fourier coefficients of HBT() oscillations

0th-order FC: centrality & kT dependence mirrors -integrated analyses; quantitatively consistent

Relative amplitudes increase from central to peripheral collisions

means relative amplitudes

STAR Collaboration, nucl-ex/0312009

• Freeze-out eccentricity can be estimated from relative amplitudes

• Blast-wave: rel. amplitudes sensitive to spatial anisotropy, depend weakly on collective flowRetiere and Lisa, nucl-th/0312024

• Freeze-out eccentricity can be estimated from relative amplitudes

• Blast-wave: rel. amplitudes sensitive to spatial anisotropy, depend weakly on collective flowRetiere and Lisa, nucl-th/0312024

20,

22,

20,

22,

20,

22,

22

22

222s

o

s

os

s

s

xy

xy

R

R

R

R

R

R

RR

RR

no temporal component

Sergey Panitkin

Comparison to PHENIXAuAu 200 GeV 30% Centrality

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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)

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qout

qside

qlong

Hanbury Brown-Twiss interferometry

Rsi

de

R long

Rout

x1

x2

12 ppq

p1

p2

q

12 pp2

1k

Two-particle interferometry: p-space separation space-time separation

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):