Two Particle Interferometry at RHIC

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Two Particle Interferometry at RHIC
Sergey Panitkin (Brookhaven National Laboratory)
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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

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Pratt-Bertsch Parameterization

Decomposition of the pair relative momentum
(measured in the LCMS frame (p1 p2)z0)

• Information
• geometrical source size Rside
• lifetime
• (for simple sources!)

Rside2R0ut2-(bpairt)2
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Pion Correlation Functions at RHIC
STAR 130 GeV
Open symbols No Coulomb Solid Coulomb
corrected Red line Gaussian fit
Experimental effects that were evaluated Single
track cuts Track merging Track splitting PID
Impurities Finite radius Coulomb Momentum
resolution Event vertex mixing
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In Search of the QGP. Naïve expectations
QGP has more degrees of freedom than pion
gas Entropy should be conserved during fireball
evolution Hence Look in hadronic phase for
signs of Large size, Large
lifetime, Expansion
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In search of the QGP Expectations

• Naïve picture (no space-momentum correlations)
  
• Rout2Rside2(bpairt)2
• One step further
• Hydro calculation of Rischke Gyulassy expects
  Rout/Rside 2-gt4 _at_ kt 350 MeV.
• Looking for a soft spot

Rside
Rout
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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 between SPS and RHIC !
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The Rout/Rside Ratio at 130 GeV
(S. Soff et al)
Hydro UrQMD
STAR
Smaller observed ratio than expected from
theory. Different KT dependence. Data -gt Short
freeze-out Model -gt Extended freeze-out
ERHIC HBT Puzzle
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RHIC HBT PUZZLE
Small Rout implies small Dt
P.Kolb
Small Rbeam implies small lifetime t, 10 fm/c
Large Rside implies large R
But Hydro fits spectra and v2 nicely!
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RHIC HBT Puzzle
Most reasonable models still do not reproduce
RHIC vSNN 130GeV HBT radii
Hydro RQMD
PHENIX PRL 88 192302 (2002)
vSNN 130GeV

• 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)

from spectra, v2
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PHENIX kT dependence of source radii
Centrality is in top 30
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PHENIX Centrality dependence _at_ 200 GeV
0.2ltkTlt2.0GeV/c, ltkTgt0.46GeV/c
Fit with p0p1Npart1/3
Rlong increases more rapidly with the Npart than
Rout.
Rlong Rside
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Centrality and mT dependence at 200 GeV
STAR PRELIMINARY
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)
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Comparison to 130 GeV. Transverse radii
STAR PRELIMINARY

• 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

Statistical errors only
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Rout/Rside Ratios at 200 GeV
Ratio is lt1 at high Pt (but note different
centralities!)
Errors are statistical systematic
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Evolution timescale from RL
Simple Mahklin/Sinyukov fit (assuming
boost-invariant longitudinal flow)
Makhlin and Sinyukov, Z. Phys. C 39 (1988) 69
Assuming TK110 MeV(from spectra at 130 GeV)
STAR PRELIMINARY
(fit to STAR 200GeV data only)
Longitudinal radius at 200GeV identical to 130
GeV
rapid evolution!!!
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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
• ltrgt 0.6
• R 12 fm
• t010 fm/c
• Rout/Rside described by sharp radial cut-off and
  brief emission duration, Dt2 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
DCA between daughters
DCA of V0 to primary vertex
DCA of daughters to primary vertex
Decay Length
DCA distance of closest approach
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K0sK0s Correlations from STAR

• no coulomb interaction
• less affected by long-lived resonance feed-down
• extend systematic to higher pT
• strangeness dynamics
• unique measurement

A promising low-Q correlation!
l0.76 ? 0.29 Rinv5.75 1.0 fm
Large source for ltmTgt 1.12 GeV/c2
??? systematic study underway
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Summary

• Lots of new data from all RHIC experiments !
• So far no obvious inconsistencies in pion HBT
  data
• pp 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 ?t
• RL (mT) Sinyukov fits ? evolution time lttgt
  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!

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Fireball dynamics Collective expansion
Shape of the mT spectrum depends on particle
mass Inverse-slope depends on mT-range
where
and
Description of freeze-out inspired by
hydrodynamics
Flow profile used ?r ?s (r/R)0.5
The model is from E.Schenedermann et al. PRC48
(1993) 2462 and based on Blast wave model
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Blast wave at 200 GeV Fails?
From the spectra (systematic errors) ?T 0.7
0.2 syst. Tfo 110 ? 23 syst. MeV
J. Burward-Hoy(QM2002)
PHENIX Preliminary
Rs (fm)
Ro (fm)
RL (fm)
?-?-
R 9.70.2 fm
?0 13?2 fm/c

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

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