Correlations, Fluctuations and Flow at STAR

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Correlations, Fluctuations andFlow at STAR

• Lanny Ray
• The University of Texas at Austin
• for The STAR Collaboration

• 419 Collaborators
• 44 Institutions
• 9 Countries
• Spokesperson Tim Hallman

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AA Dynamics QM Interference
Similar Effects for all events - Static
Non-Statistical EbyE Fluctuations
Observed Correlations
New Physics, e.g. - EOS - Color
deconfinement -Chiral Symm. Rest.
Source Phenomenology
(See talks by G. Van Buren, G. Kunde, D. Hardtke,
S. Voloshin, K. Filimonov)
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Source Phenomenology
Bose-Einstein (pions, kaons)
Observed p (mT,y,f) Source x (r,j,h,t) Local
temperature, T Bjorken expansion trans.
flow field, u(x) Space-time modulation,
F Chemical potential, m
Spectra HBT radii ltfgt v2 (fluctuations)
S(x,p)
Blast wave - a simpler source - freezeout wrt
long. proper time - integrates over all y -
longitudinally invariant wrt h
Tomasik, Wiedemann, Heinz, nucl-th/9907096. Tomas
ik Heinz, PRC 65, 031902 (2002). Schnedermann,
Sollfrank, Heinz, PRC 48, 2462 (1993).
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Two-Pion HBT for AuAu at 130 and 200 GeV
(see Talk by M. Lopez-Noriega)
Radii increase with centrality decrease with
increasing ltmTgt
RO/RS lt 1
Sinyukov fits At0 (source lifetime) t0
(central) 10 fm/c t0 (midcentral) 9 fm/c t0
(peripheral) 8 fm/c
(Makhlin and Sinyukov, Z.Phys. C39, 69 (1988))
STAR Preliminary
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Three Pion HBT at STAR - Chaotic Sources for
AuAu at 130 GeV
Two-pion HBT - llt1 due to coherence and
contamination Combined 2-,3-pion HBT measures
degree of chaoticity of source U. Heinz and Q.H.
Zhang, PR C 56, 426 (1997)
p p-
Central p-p-p-
Limit at Q30
STAR Preliminary
Approaches fully chaotic source
STAR Preliminary
(see Talk by R. Willson)
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Pion Phase Space Density for AuAu at 130 GeV
G. Bertsch, PRL 72, 2349 (1994)
PRL 77, 789(E) (1996). D. Ferenc et al., Phys.
Lett. B 457, 347 (1999).
NA49 PbPb central Ferenc et al., Phys. Lett.
B457, 347 (1999)
Pion Laser???
Bose-Einstein fit to p- spectra
central
STAR Preliminary
ltfgt
peripheral
pT
mT-mp
ltfgt(RHIC) gt ltfgt(SPS)
(see Poster by John Cramer)
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Non-Identical (pK) Correlations
R. Lednicky et al., Phys. Lett. B373, 30 (1996)
C
p
K-

• Coulomb interaction
• Similar transverse velocities
• Analysis selects C(vpgtvK)
• or C-(vpltvK)
• Form ratio C/C-
• vTransverse 0.7-0.8c due to TPC
• PID dE/dx limitations
• Year 2000 data with hlt0.5,
• Top 12 central events

For this example C/C- gt 1
C-
p
K-
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Correlation Functions and Ratios for pK AuAu at
130 GeV
CF
Similar K and K- emission
C/C-
C/C-
pK source asymmetry
Out
STAR Preliminary
Occurs more often than
Side

• 1

Long
kpair cm
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Blast Wave Interpretation

• Parameters fitted to p,K,p spectra
• and pion HBT radii
• T110 MeV, ltrgt0.6, R13 fm
• Short emission duration, D t 1.5 fm/c
• Larger thermal dispersion of pion
• emission region than for kaons

DRLAB -4.6 fm
C/C-
(see Posters by Adam Kisiel, Piotr Szarwas, Talk
by F. Retiere)
STAR Preliminary
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What have we learned about 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
• (box shape) and brief emission duration,
• Dt2 fm/c which squeezes Rout
• Increased pion PSD, multi-pion effects (?)
• Azimuthal dependence (see following)

• But our analysis is not
• particularly sensitive to
• - Transverse expansion profile
• - Details of longitudinal boost
• and shape (y0)
• - Chemical potential strength
• - Details of the freeze-out
• hypersurface space-time
• geometry
• Except as it affects yields
• Also, fluctuation effects are
• not yet included in source
• model (e.g. DT, Dltrgt) .

(see Poster by Masashi Kaneta)
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Longitudinal Correlations
Two-particle correlations projected onto 2D
pseudorapidity space
Construct the Charge Difference, invariant wrt
h1h2, Strong CD correlations wrt h1-h2
h2
h1
CI ()(--)(-)(-) CD
()(--)-(-)(-)
Flip sign Balance Function
Project
STAR Preliminary
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Balance Function Analysis
Bass, Danielewicz, Pratt, Phys. Rev. Lett. 85,
2689 (2000)

• Motivated by the idea that hadrons
• are locally produced in (),(-) pairs.
• Early pairs separate due to Long. Exp.
• Later pairs correlated at small Dy

N - (Dy) Histogram of y(p) - y(p-) , for
all possible pairs within an event. This
histogram is summed over all events.
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Balance Function Widths for AuAu at 200 GeV
Narrows with centrality - transverse boost -
additional resonances(?) - late hadronization(?)
STAR Preliminary
(see Poster by Gary Westfall)
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Azimuthal Angle Correlations for AuAu at 130 GeV
Like sign
Unlike sign
Two-particle correlations projected onto f1? f2
space
Project these onto f1-f2 difference Elliptic Flow
is apparent but Large non-flow CI and CD
components 4-particle azimuthal angle
correlations are now used to determine v2
STAR Preliminary
STAR Preliminary
(no merging corrections)
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Measuring Azimuthal Anisotropy - Elliptic Flow

• Borghini,Dinh, Ollitrault, PRC 63, 054906 (2001)
  proposed 4-particle
• azimuthal correlation analysis, using
  cumulant expansion, to remove
• non-flow contributions from v2.
• Implemented for STAR flow analysis used for 130
  200 GeV data.

2-part
4-part

• 15 Non-Flow contribution need more statistics
  at higher pT
• v2 increases 7-10 at 200 GeV (not shown)
• Simulations show 4-particle analysis stable
  against embedded
• 4-particle correlated clusters

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Approaching Local Thermal Equilibrium?
v2/e
Initial eccentricity
Const. cs
x
At RHIC Energies
Hydro Limit QGP EOS, lltltR
Low Density Limit, lR
AGS SPS RHIC
v2(b) v2(pT)
OK-cent. only OK,pTlt2GeV/c
OK Poor
(see Talk by Sergei Voloshin)
Teaney,Lauret,Shuryak nucl-th/0110037 Heiselber
gLevy,PRC 59, 2716 (1999)
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HBT with respect to Event Plane
Minbias AuAu at 130 GeV summed p and p-
Blast wave model
T100 MeV,?r0?0.6 R11.7 fm, Dt2.2
fm/c ?ra?0.037, ?s2?0.037
STAR Preliminary

• Same parameters fit R(f) and v2(pT,m)
• Spatial anisotropy dominates R(f)
• Amplitude 1/10 AGS (E895) value
• Source is out-of-plane extended
• Opposite from HydroRQMD prediction

(see Talk by M. Lopez-Noriega)
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Fluctuations - Transverse Momentum Correlations
Boltzmann
Lévy
Fluctuating T,bT alters the shape of the mT
spectrum
DT
dN/mTdmT
mT
mT
mT?mT Ratio of real pairs/mixed
pairs integrated over h,f
DT,DbT
AuAu at 130 GeV 70K Central events 0.15 lt pT lt 2
GeV/c h lt 1.3 All charges
1
1
X(mT2)
X(mT1)
High mT
0
Low mT
HBT, Coulomb
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Fluctuations in mean-pT for AuAu at 130 GeV
Nonstatistical fluctuations increase the rms
width by 140.5
Gamma with increased rms Gamma ref. from
inclusive pT spectrum
183K top 15 central events using 70 of all
primary particles Both () and (-) charges h lt
1, full f 0.1 lt pT lt 2.0 GeV/c
Reference studies continuing - mixed event
reference - N sampled inclusive spectrum - Both
are consistent with Gamma
STAR Preliminary
In units of expected rms from CLT
Centered at 0
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Numerical measures of mean-pT fluctuations
Extrapolation to 100
CI
70 of primaries
STAR Preliminary
CD x 3
centrality

• Strong NonStat fluctuations
• Centrality dependence
• CI larger than at SPS
• CD smaller at RHIC
• PHENIX null result is not inconsistent with
  STARs measurement

CI ()(--)(-)(-) CD
()(--)-(-)(-)
205K minbias events 70 of primaries Extrapolated
to 100 0.5 MeV/c stat. errors 20 syst.
Errors DCA cut lt 3 cm
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Net Charge Fluctuations in AuAu at 130 and 200
GeV
Predicted to be reduced in QGP due to q gt h and
fractional charge
Quantitative measure
Nn -, dyn
Poisson
50K minbias, 80K central Dh 0.5 bins in
hlt0.75 0.1lt pTlt5 GeV/c

• 130 GeV
• 200 GeV

Charge conserv.
pp
Motivated in papers by Jeon, Koch, Bleicher -
PRL 83, 5435 (1999) - PRL 85, 2076 (2000) - PRC
62, 061902 (2000)
STAR Preliminary
Resonance gas
Fast hadronizing QGP at -3.5
(see Poster by Claude Pruneau)
centrality
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Summary and Conclusions

• Wealth of new correlation, flow and EbyE
  fluctuation data from STAR
• No big surprises, so far, in the 200 GeV AuAu
  data
• compared to the 130 GeV data
• New analysis methods developed for NonID
  particles, flow, fluctuations
• Source phenomenology making progress
• Compared to AGS SPS, RHIC events display
• - similar HBT radii (regions of homogeneity)
• - higher pion PSD
• - stronger v2/e
• - stronger CI ltpTgt fluctuations weaker CD.
• - stronger radial boost with brief emission
  duration
• - same (as AGS) out-of-plane extended source
  but 1/10 amplitude
• Hydro-models
• - v2(pT,m) to 2 GeV/c, v2/e, source extension
  wrt RP, spectra shapes
• - HBT radii, fluctuations(?)