Sergey Panitkin

Two Particle Interferometry at RHIC

Sergey Panitkin

(Brookhaven National Laboratory)

Sergey Panitkin

Outline

Introduction and Motivation Summary of Results from AuAu 130 GeV Results from AuAu 200 GeV

– PHOBOS– PHENIX– STAR (see talks by M. Lisa, V. Okorokov)

Summary and outlook

Sergey Panitkin

Information:

•geometrical source size: Rside

•lifetime

(for simple sources!)

)( 222222

1),,( LongLongSideSideOutOut RqRqRqLongSideOut eqqqC

px

qOutpy

qSideDecomposition of the pair relative momentum

(measured in the LCMS frame; (p1+ p2)z=0)

Pratt-Bertsch Parameterization

Rside2=R0ut

2-(pair)2

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Pion Correlation Functions at RHIC

Open symbols – No Coulomb

Solid – Coulomb corrected

Red line – Gaussian fit

Experimental effects that were evaluated:Single track cutsTrack mergingTrack splittingPID Impurities

Finite radius CoulombMomentum resolutionEvent vertex mixing

STAR 130 GeV

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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

“Naïve” picture (no space-momentum correlations):

– Rout2=Rside

2+(pair)2

One step further:– Hydro calculation of Rischke

& Gyulassy expects Rout/Rside ~ 2->4 @ kt = 350 MeV.

– Looking for a “soft spot”

Rout

Rside

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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

Note ~100 GeV gap betweenSPS and RHIC !

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The Rout/Rside Ratio at 130 GeV

Hydro +UrQMD

Smaller observed ratio than expected from theory.

Different KT dependence.Data -> Short freeze-outModel -> Extended freeze-out

(S. Soff et al)

RHIC HBT Puzzle

STAR

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RHIC HBT PUZZLE

P.Kolb

Small Rout implies small

Large Rside implies large RSmall Rbeam impliessmall lifetime ~10 fm/c

But Hydro fits spectra and v2 nicely!

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RHIC HBT Puzzle

Most “reasonable” models still do not reproduce RHIC √SNN = 130GeV HBT radii

“Blast wave” parameterization (Sollfrank

model) can approximately describe data at 130

GeV

…but emission duration must be small

= 0.6 (radial flow)

• T = 110 MeV

• R = 13.5 1fm (hard-sphere)

emission= 1.5 1 fm/c (Gaussian)

fromspectra, v2

√SNN = 130GeVPHENIX PRL 88 192302 (2002)

STAR 130 GeV

PHENIX 130 GeV

Hydro + RQMD

+-

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PHENIX kT dependence of source radiiCentrality is in top 30%

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PHENIX Centrality dependence @ 200 GeV

Fit with p0+p1*Npart^1/3

Rlong increases more rapidly with the Npart

than Rout.

0.2<kT<2.0GeV/c, <kT>=0.46GeV/c

Rlong ~ Rside

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Centrality and mT dependence at 200 GeV

RL varies similar to RO, RS with centrality

HBT radii decrease with mT (flow)

Roughly parallel mT dependence for different centralities

RO/RS ~ 1 (short emission time)

Central

Midcentral

Peripheral

200GeV

STAR PRELIMINARY

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Comparison to 130 GeV. Transverse radii

*

Central

Midcentral

Peripheral

PHENIX Central

200GeV - 130 GeV

Higher B-field higher pT

Transverse radii:

• similar but not identical• low-pT RO, RS larger at 200 GeV• steeper falloff in mT

(PHENIX 130GeV)• Ro falls steeper with mT

STAR PRELIMINARY

Statistical errors only

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Rout/Rside Ratios at 200 GeV

Ratio is <1 at high Pt (but note different centralities!)

Errors are statistical + systematic

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Evolution timescale from RL

(fit to STAR 200GeV data only)

Simple Mahklin/Sinyukov fit (assuming boost-invariant longitudinal flow)

T

KfoL m

TtR

Assuming TK=110 MeV(from spectra at 130 GeV)

fm/c 6.7t

fm/c 10t

periphfo

centralfo

Makhlin and Sinyukov,

Z. Phys. C 39 (1988) 69

STAR PRELIMINARY

Longitudinal radius:at 200GeV identical to 130 GeV

rapid evolution!!!

*

Central

Midcentral

Peripheral

PHENIX Central

200GeV - 130 GeV

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What have we learned about pion source S(x,p) ?

Pion spectra shapes plus HBT RO,S,L(KT): T ~ 100 MeV <> ~ 0.6 R ~ 12 fm t0~10 fm/c Rout/Rside described by sharp radial cut-off and brief emission duration, ~2 fm/c which squeezes Rout

Increased pion phase space density (see talk by R. Lednicky)Azimuthal dependence points toward fast break up of the source (see talk by M. Lisa)

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Comparison of kaons to pions

In the most 30% central

Mt scaling violation ?

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STAR K0s Reconstruction

Number of K0s

Mean ~ 3.79 / Event

Nu

mb

er o

f ev

entsDCA – distance of closest approach

pT(GeV/c)

pT ~ 1 GeV/cmT ~ 1.12 GeV/c2c

ou

nts

DCA between daughters

DCA of daughters to primary vertex

DCA of V0 to primary vertex

Decay Length

Vo

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K0sK0

s Correlations from STAR

STAR PRELIMINARY

S/N = 19.11

Minv (GeV/c2)

cou

nts

0.46 0.48 0.50 0.52

blue: signal from fit

red : noise

A promising low-Q correlation!

Qinv (GeV/c)

CF STAR PRELIMINARY

• no coulomb interaction

• less affected by long-lived resonance feed-down

• extend systematic to higher pT

• strangeness dynamics

• unique measurement

Large source for <mT> ~ 1.12 GeV/c2 ???systematic study underway…

=0.76 0.29Rinv=5.75 ± 1.0 fm

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Summary

Lots of new data from all RHIC experiments ! So far no obvious inconsistencies in pion HBT data

interferometry:

sources sizes at 200 roughly same as at 130GeV, with similar systematics:

radii decrease with mT: consistent with radial flow mT dependence independent of centrality

RO/RS ~ 1 over large Pt range: short emission duration RL (mT): Sinyukov fits → evolution time: <> ≈ 10fm/c systematics study underway

Kaon interferometry: Mt scaling violation (Charged kaons –PHENIX, K0 – STAR) ? More data needed (coming soon!)

More data to come soon ! Need theoretical explanation!

Sergey Panitkin

Fireball dynamics: Collective expansion

tanh 1 r r (r) s f (r)

R

s

Flow profile used

r =s (r/R)0.5

dn

mT dmT r dr mT K1

mT coshT

0

R

I0pT sinh

T

Shape of the mT spectrum depends on particle mass

Inverse-slope depends on mT-range

where and

The model is from E.Schenedermann et al. PRC48 (1993) 2462 and based on Blast wave model

Description of freeze-out inspired by hydrodynamics

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Blast wave at 200 GeV: Fails?

10% central negative pion HBT radii. Systematic uncertainty in the data is 8.2% for Rs, 16.1% for Ro, 8.3% for RL.

From the spectra (systematic errors):T = 0.7 ± 0.2 syst. Tfo = 110 23 syst. MeV

--

0 = 132 fm/cR = 9.7±0.2 fm

PHENIX PreliminaryRs (fm) Ro (fm) RL (fm)

J. Burward-Hoy(QM2002)

Model by Wiedemann, Scotto, Heinz, PRC 53 (No. 2), Feb. 1996