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Two Particle Interferometry at RHIC. Sergey Panitkin (Brookhaven National Laboratory). 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. q Side. q Out. p y.

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two particle interferometry at rhic
Two Particle Interferometry at RHIC

Sergey Panitkin

(Brookhaven National Laboratory)

Sergey Panitkin

outline
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

pratt bertsch parameterization

qSide

qOut

py

px

Pratt-Bertsch Parameterization

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

pion correlation functions at rhic
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

in search of the qgp na ve expectations
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

in search of the qgp expectations
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 ~ 2->4 @ kt = 350 MeV.
    • Looking for a “soft spot”

Rside

Rout

Sergey Panitkin

excitation function of the hbt parameters
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

the r out r side ratio at 130 gev

The Rout/Rside Ratioat 130 GeV

(S. Soff et al)

Hydro +UrQMD

STAR

Smaller observed ratio than expected from theory.

Different KT dependence.

Data -> Short freeze-out

Model -> Extended freeze-out

ERHIC HBT Puzzle

Sergey Panitkin

rhic hbt puzzle
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

rhic hbt puzzle1

STAR 130 GeV

PHENIX 130 GeV

p +

p -

RHIC HBT Puzzle

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

Hydro + RQMD

PHENIX PRL 88 192302 (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  1fm/c (Gaussian)

from

spectra, v2

Sergey Panitkin

phenix kt dependence of source radii
PHENIX kT dependence of source radii

Centrality is in top 30%

Sergey Panitkin

phenix centrality dependence @ 200 gev
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

centrality and m t dependence at 200 gev

200GeV

Central

Midcentral

Peripheral

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)

Sergey Panitkin

comparison to 130 gev transverse radii

200GeV - 130 GeV

Central

Midcentral

Peripheral

PHENIX Central

*

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

Sergey Panitkin

r out r side ratios at 200 gev
Rout/Rside Ratios at 200 GeV

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

Errors are statistical + systematic

Sergey Panitkin

evolution timescale from r l

200GeV - 130 GeV

Central

Midcentral

Peripheral

PHENIX Central

*

Evolution timescale from RL

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

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

what have we learned about pion source s x p
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

comparison of kaons to pions
Comparison of kaons to pions

In the most 30% central

Mt scaling violation ?

Sergey Panitkin

star k 0 s reconstruction

Vo

Mean ~ 3.79 / Event

pT ~ 1 GeV/c

mT ~ 1.12 GeV/c2

counts

Number of events

Number of K0s

pT(GeV/c)

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

Sergey Panitkin

k 0 s k 0 s correlations from star

blue: signal from fit

red : noise

S/N = 19.11

counts

CF

STAR PRELIMINARY

STAR PRELIMINARY

0.46

0.48

0.50

0.52

Minv (GeV/c2)

Qinv (GeV/c)

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!

l=0.76 0.29

Rinv=5.75 ± 1.0 fm

Large source for <mT> ~ 1.12 GeV/c2 ???

systematic study underway…

Sergey Panitkin

summary
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: <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

fireball dynamics collective expansion

b s

R

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) 2462and based on Blast wave model

Sergey Panitkin

blast wave at 200 gev fails
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)

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

--

R = 9.7±0.2 fm

0 = 132 fm/c

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

Sergey Panitkin