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

2. 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

3. Pratt-Bertsch Parameterizationpx
qOut py
qSide
Decomposition of the pair relative momentum
(measured in the LCMS frame; (p1+ p2)z=0)
Information:
geometrical source size: Rside
lifetime
(for simple sources!)
Rside2=R0ut2-(bpairt)2
Sergey Panitkin

4. 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
Sergey Panitkin

5. 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……
Sergey Panitkin

6. In search of the QGP: Expectations
“Naïve” picture (no space-momentum correlations):
Rout2=Rside2+(bpairt)2
One step further:
Hydro calculation of Rischke & Gyulassy expects Rout/Rside ~ kt = 350 MeV.
Looking for a “soft spot”
Rside
Rout
Sergey Panitkin

7. 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 !
Sergey Panitkin

8. The Rout/Rside Ratio at 130 GeV
Hydro +UrQMD
(S. Soff et al)
STAR
Smaller observed ratio than expected from theory.
Different KT dependence.
Data -> Short freeze-out
Model -> Extended freeze-out
ERHIC HBT Puzzle
Sergey Panitkin

9. But Hydro fits spectra and v2 nicely!
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!
Sergey Panitkin

10. RHIC HBT Puzzle
Most “reasonable” models still do not reproduce RHIC √SNN = 130GeV HBT radii
Hydro + RQMD
STAR 130 GeV
PHENIX 130 GeV
p +
p -
PHENIX PRL (2002)
√SNN = 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
Sergey Panitkin

11. PHENIX kT dependence of source radii
Centrality is in top 30%
Sergey Panitkin

12. PHENIX Centrality dependence @ 200 GeV
0.2<kT<2.0GeV/c, <kT>=0.46GeV/c
Fit with
p0+p1*Npart^1/3
Rlong increases more rapidly with the Npart than Rout.
Rlong ~ Rside
Sergey Panitkin

13. Centrality and mT dependence at 200 GeV
Midcentral
Peripheral
200GeV
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 ~ (short emission time)
Sergey Panitkin

14. Comparison to 130 GeV. Transverse radii
STAR PRELIMINARY *
Central
Midcentral
Peripheral
PHENIX Central
200GeV 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
Boris is a great guy!
Statistical errors only
Sergey Panitkin

15. Rout/Rside Ratios at 200 GeV
Ratio is <1 at high Pt (but note different centralities!)
Errors are statistical + systematic
Sergey Panitkin

16. Evolution timescale from RL
Simple Mahklin/Sinyukov fit (assuming boost-invariant longitudinal flow) *
Central
Midcentral
Peripheral
PHENIX Central
200GeV GeV
Makhlin and Sinyukov,
Z. Phys. C 39 (1988) 69
Assuming TK=110 MeV (from spectra at 130 GeV)
STAR PRELIMINARY
(fit to STAR 200GeV data only)
Longitudinal radius:
at 200GeV identical to 130 GeV
rapid evolution!!!
Sergey Panitkin

17. What have we learned about pion source S(x,p) ?
Pion spectra shapes plus HBT RO,S,L(KT):
T ~ 100 MeV
<r> ~ 0.6
R ~ 12 fm
t0~10 fm/c
Rout/Rside described by sharp radial cut-off and brief emission duration, Dt~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)
Sergey Panitkin

18. Comparison of kaons to pions
In the most 30% central
Mt scaling violation ?
Sergey Panitkin

19. STAR K0s Reconstruction
DCA between daughters Vo
DCA of V0 to primary vertex
DCA of daughters to primary vertex
Decay Length
Number of K0s
Mean ~ 3.79 / Event
Number of events
DCA – distance of closest approach
pT(GeV/c)
pT ~ 1 GeV/c
mT ~ 1.12 GeV/c2
counts
Sergey Panitkin

20. K0sK0s Correlations from STAR
STAR PRELIMINARY
S/N = 19.11
Minv (GeV/c2)
counts
0.46
0.48
0.50
0.52
blue: signal from fit
red : noise
no coulomb interaction
less affected by long-lived resonance feed-down
extend systematic to higher pT
strangeness dynamics
unique measurement
Qinv (GeV/c) CF
STAR PRELIMINARY
A promising low-Q correlation!
l=0.76  0.29
Rinv=5.75 ± 1.0 fm
Large source for <mT> ~ 1.12 GeV/c2 ???
systematic study underway…
Sergey Panitkin

21. Summary pp interferometry:
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: <t> ≈ 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

22. 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 R
b s
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
Sergey Panitkin

23. 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 = 9.7±0.2 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
Sergey Panitkin