Dynamics at low and high pT from the
Solenoidal Tracker At RHIC (STAR)
Mike Lisa, Ohio State University
STAR Collaboration
U.S. Labs: Argonne, Lawrence Berkeley
National Lab, Brookhaven National Lab
U.S. Universities: Arkansas, UC Berkeley,
UC Davis, UCLA, Carnegie Mellon,
Creighton,
Indiana,
Kent State,
Michigan State,
CCNY,
Ohio State,
Penn State,
Purdue, Rice,
Texas A&M,
UT Austin,
Washington,
Wayne State,
Yale
STAR
Brazil:
Universidade de Sao Paolo
China:
IHEP - Beijing, IPP - Wuhan
England: University of Birmingham
France: Institut de
Recherches Subatomiques
Strasbourg, SUBATECH Nantes
Germany: Max Planck
Institute – Munich,
University of Frankfurt
Poland: Warsaw University,
Warsaw University of
Technology
Russia: MEPHI – Moscow,
LPP/LHE JINR–Dubna,
IHEP-Protvino
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
1
Outline
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
starting slow & ending fast
• General goal of RHIC physics
• RHIC & STAR
hadro-chemistry
• driving dynamical physics and consistent picture @ low pT?
– central collisions
radial flow
• two-particle correlations
 HBT
K- correlations
balance functions
– non-central collisions
elliptical flow
HBT vs reaction-plane
– low-pT summary
• driving physics @ “high” pT?
spectra compared to pp collisions
momentum-space anisotropy
two-particle correlations
• Summary
2
Why heavy ion collisions?
The “little bang”
• Study bulk properties of nuclear matter
• Extreme conditions
(high density/temperature) expect a transition
to new phase of matter…
• Quark-Gluon Plasma (QGP)
• partons are relevant degrees of freedom over
large length scales (deconfined state)
• believed to define universe until ~ ms
• Study of QGP crucial to understanding QCD
• low-q (nonperturbative) behaviour
• confinement (defining property of QCD)
• nature of phase transition
• Heavy ion collisions ( “little bang”)
• the only way to experimentally probe
deconfined state
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
3
Stages of the collision
“end result” looks very similar
whether a QGP was formed or not!!!
The “little bang”
• pre-equilibrium (deposition of initial energy)
• rapid (~1 fm/c) thermalization (?)
• high-pT observables probe this stage
time
hadronization transition
(very poorly understood)
hadronic rescattering
temperature
QGP formation (?)
Chemical freeze-out: end of inelastic scatterings
Kinetic freeze-out: end of randomizig scatterings
• low-pT hadronic observables probe this stage
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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STAR
The “little bang”
Experimentally calibrating time, temperature
“axes”
• critical to gaining insight into physics of
extreme nuclear conditions
• provides a stringent test of dynamical models
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
temperature
time
Stages of the collision
5
Already producing QGP at lower energy?
Thermal model fits to particle yields
(including strangeness, J/)
 approach QGP at CERN?
J. Stachel, Quark Matter ‘99
• is the system really thermal?
• warning: e+e- falls on similar line!!
• dynamical signatures? (no)
• what was pressure generated?
• what is Equation of State of
strongly-interacting matter?
Must go beyond chemistry:
 study dynamics of system well into
deconfined phase (RHIC)
lattice QCD applies
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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uRQMD simulation of Au+Au @ s=200 GeV
pure hadronic & string
description (cascade)
generally OK at lower
energies
applicability in very high
density (RHIC) situations
unclear
produces too little
collective flow at RHIC
freeze-out given by last
hard scattering
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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The Relativistic Heavy Ion Collider (RHIC)
at Brookhaven National Laboratory (BNL)
Colliding Au beams: 65 GeV + 65 GeV (s=130 GeV)
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Geometry of STAR
Magnet
Coils
TPC Endcap
& MWPC
Time
Projection
Chamber
Silicon
Vertex
Tracker
FTPCs
ZCal
ZCal
Endcap
Calorimeter
Barrel EM
Calorimeter
Vertex
Position
Detectors
Central Trigger
Barrel or TOF
RICH
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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STAR Time Projection
Chamber (TPC)
• Active volume: Cylinder r=2 m, l=4 m
– 139,000 electronics channels
sampling drift in 512 time buckets
– active volume divided into 70M
3D pixels
On-board FEE Card:
Amplifies, samples,
digitizes 32 channels
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Peripheral Au+Au Collision at 130 AGeV
Data Taken June 25, 2000.
Pictures from Level 3 online display.
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Au on Au Event at CM Energy ~ 130 AGeV
Data Taken June 25, 2000.
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Particle ID in STAR
RICH
STAR
dE/dx
dE/dx PID range:
[s (dE/dx) = .08]
RICH PID range:
p  ~ 0.7 GeV/c for K/
1 - 3 GeV/c for K/
 ~ 1.0 GeV/c for p/p
Topology
1.5 - 5 GeV/c for p/p
Decay vertices
Ks   + +  -
L  p +-
L  p +  +
X +
L +  +
Combinatorics
Ks   + +  -
f  K++K-
X- L + -
L  p + -
L  p +  +
W  L + K-
[ r   + +  -]
[D  p +  -]
dn/dm
f from K+ K- pairs
background
subtracted
Vo
m inv
dn/dm
same event dist.
mixed event dist.
“kinks”:
K m + 
STAR
K+ K- pairs
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
m 13
inv
Kaon Spectra at Mid-rapidity vs Centrality
K-
K+
Centrality
cuts
Centrality
cuts
STAR preliminary
Exponential fits to mT spectra:
STAR
(K++K-)/2
Ks
STAR preliminary
1 dN
 m 
 A exp   T 
mT dmT
 T 
Centrality
cuts
STAR preliminary
Good agreement between
different PID methods
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Statistical Thermal Model: Fit Results
• T ~170 MeV (sim SPS): saturation?
• mb ~ 45 MeV (lower than SPS)
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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First RHIC spectra - an explosive source
• various experiments agree well
T
explosive
source
T,b
STAR
1/mT dN/dmT
purely thermal
source
1/mT dN/dmT
• different spectral shapes for
particles of differing mass
 strong collective radial flow
light
heavy
mT
light
heavy
mT
• very good agreement with hydrodynamic
prediction
data: STAR, PHENIX, QM01
Warsaw STAR/ALICE HBT Workshop - May 2002 -model:
malisa P. Kolb, U. Heinz 16
Hydrodynamics: modeling high-density scenarios
• Assumes local thermal equilibrium (zero mean-free-path limit) and solves
equations of motion for fluid elements (not particles)
• Equations given by continuity, conservation laws, and Equation of State (EOS)
• EOS relates quantities like pressure, temperature, chemical potential, volume
– direct access to underlying physics
• Works qualitatively at lower energy
but always overpredicts collective
effects - infinite scattering limit
not valid there
– RHIC is first time hydro works!
STAR
lattice
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
QCD input
17
Thermal motion superimposed on radial flow
Hydro-inspired “blast-wave”
thermal freeze-out fits to , K, p, L
bs
R
preliminary
s
u (t , r , z  0)  (cosh r , er sinh r , 0)
r  tanh 1 br
b r  b s f (r )
Tth = 107 MeV
b = 0.55
M. Kaneta
E.Schnedermann et al, PRC48 (1993) 2462
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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The other half of the story…
• Momentum-space characteristics of freeze-out appear well understood
• Coordinate-space ?
• Probe with two-particle intensity interferometry (“HBT”)
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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“HBT 101” - probing source geometry
p1
 source
r(x)
1m
x2
p2
5 fm
r2
T 
  
  i( r2  x 2 )p 2
i ( r1  x1 )p1
1 {  
U(x1, p1)e
U(x 2 , p2 )e
2
  i( r1  x 2 )p1   i( r2  x 1 )p 2
 U(x 2 , p1)e
U(x1, p2 )e
}

*TT  U1*U1  U*2 U 2  1  eiq( x1  x 2 )
2-particle probability
P(p1, p 2 )
2
C(p1, p 2 ) 
 1 ~
r (q )
P(p1 )P(p 2 )
1-particle probability
r(x,p) = U*U
C (Qinv)
r1
x1

  
q  p 2  p1
Width ~ 1/R
2
1
Measurable!
STAR
F.T. of pion source
0.05
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
0.10
20
Qinv (GeV/c)
“HBT 101” - probing the timescale of emission
C(qo , qs , ql )  1    e 
 q o2 R o2  q s2 R s2  q l2 R l2
Decompose q into components:
qLong : in beam direction
qOut : in direction of transverse momentum
qSide :  qLong & qOut
 
 
  

~2
K  ~
x out  b t 

2 
2
~
R s K  x side K

~2
2
Rl K  ~
x long  bl t
R o2
K

 

K
 
  

K
~
xx x
Rout
Rside
(beam is into board)
STAR
d 4 x  S( x, K )  f ( x )

f 
4
 d x  S( x, K )
R o2
 R s2
 b  
2
x out , x side   x, y 
beware this “helpful” mnemonic!
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Large lifetime - a favorite signal of “new” physics at
RHIC
• hadronization time
(burning log) will
increase emission
timescale (“lifetime”)
• measurements at lower
energies (SPS, AGS)
observe <~3 fm/c
with
transition
~
• magnitude of predicted
effect depends strongly
on nature of transition
3D 1-fluid Hydrodynamics
ec
Rischke & Gyulassy
NPA 608, 479 (1996)
“e”
…but lifetime determination is complicated by other factors…
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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First HBT data at RHIC
“raw” correlation function projection
Coulomb-corrected
(5 fm full Coulomb-wave)
Data well-fit by Gaussian parametrization
C(qo , qs , ql )  1    e 
 q o2 R o2  q s2 R s2  q l2 R l2

1D projections of 3D correlation function
integrated over 35 MeV/cin unplotted components
STAR Collab., PRL 87 082301 (2001)
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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HBT excitation
function
midrapidity, low pT from central AuAu/PbPb
• decreasing  parameter partially
due to resonances
• saturation in radii
• geometric or dynamic
(thermal/flow) saturation
• the “action” is ~ 10 GeV (!)
• no jump in effective lifetime
• NO predicted Ro/Rs increase
(theorists: data must be wrong)
• Lower energy running needed!?
STAR
STAR Collab.,
PRLSTAR/ALICE
87 082301 (2001)
Warsaw
HBT Workshop - May 2002 - malisa
24
Hydro attempts to reproduce data
generic
hydro
Rlong: model waits too long
before emitting
Rout
model emission timescale too long
• KT dependence approximately reproduced
 correct amount of collective radial flow
Rside
STAR
• Right dynamic effect / wrong space-time
evolution???
 the “RHIC HBT Puzzle”
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
25
Failure to reproduce HBT a generic problem
hydro evolution
later hadronic stage?
• (Almost) no dynamical model
correctly predicts HBT measurements
• The more realistic/“reasonable” a
model is, the worse it seems to do…
data
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Now what?
• “Realistic” dynamical models cannot adequately describe freeze-out distribution
• Seriously threatens hope of understanding pre-freeze-out dynamics
• Raises several doubts
– is the data consistent with itself ? (can any scenario describe it?)
– analysis tools understood?
• Attempt to use data itself to parameterize freeze-out distribution
• Identify dominant characteristics
• Examine interplay between observables (e.g. flow and HBT)
• Isolate features generating discrepancy with “real” physics models
• focus especially on timescales
• Attack problem from as many sides as possible
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
27
Blastwave parameterization:
Implications for HBT: radii vs pT
Assuming b, T obtained from spectra fits
 strong x-p correlations, affecting RO, RS differently
K
2
RO
pT=0.2
2
 RS
 b  
2
RO
K
RS
pT=0.4
STAR
“whole source” not viewed
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
28
Blastwave: radii vs pT
Using flow and temperature from spectra,
can account for observed drop in HBT
radii via x-p correlations, and Ro<Rs
…but emission duration must be small
STAR data
K
pT=0.2
Four parameters affect HBT radii
R o2  R s2  b2 2
blastwave: R=13.5 fm,
freezeout=1.5 fm/c
K
pT=0.4
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
29
Joint view of  freezeout: HBT & spectra
• common model/parameterset
describes different aspects of f(x,p)
spectra ()
STAR preliminary
• Increasing T has similar effect on a
spectrum as increasing b
• But it has opposite effect on R(pT)
 opposite parameter correlations in
the two analyses
 tighter constraint on parameters
HBT
• caviat: not exactly same model used
for this plot (different flow profiles)
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
30
From Rlong: Evolution timescale tkinetic
Simple Sinyukov formula (S. Johnson)
– RL2 = tkinetic2 T/mT
• tkinetic = 10 fm/c (T=110 MeV)
STAR
B. Tomasik (~3D blast wave)
– tkinetic = 8-9 fm/c
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Kaon – pion correlations:
dominated by Coulomb interaction
Smaller source  stronger
(anti)correlation
K-p correlation well-described by:
• Blast wave with same parameters
as spectra, HBT
But with non-identical particles, we
can access more information…
STAR preliminary
Adam Kiesel, Fabrice Retiere
STAR
Systematic program on non-identical
particle correlations spearheaded
by Warsaw group
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
32
Initial idea: probing emission-time ordering
purple K emitted first
green  is faster
• Catching up: cosY  0
•
•
purple K emitted first
green  is slower
• Moving away: cosY  0
•
•
Crucial point:
kaon begins farther in “out” direction
(in this case due to time-ordering)
STAR
long interaction time
strong correlation
short interaction time
weak correlation
• Ratio of both scenarios
allow quantitative study of
the emission asymmetry
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
33
measured K- correlations - natural consequence of
space-momentum correlations
• clear space-time asymmetry observed
• C+/C- ratio described by:
– “standard” blastwave w/ no time shift
• Direct proof of radial flow-induced
space-momentum correlations
STAR preliminary
Pion
STAR
<pt>
= 0.12 GeV/c
Kaon
<pt> =STAR/ALICE
0.42 GeV/cHBT Workshop - May 2002 - malisa
Warsaw
34
Balance functions:
How they work
For each charge +Q, there is one extra balancing charge –Q.
Charges: electric, strangeness, baryon number
Bass, Danielewicz, Pratt (2000)
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Balance functions - clocking the evolution
Bjorken
(narrow)
Pythi
a
(wide
)
Model predictions
 Wide  early creation of charges
+  nn, e e collisions
 Narrow  late hadronization / (Q)GP
 central collisions @ RHIC?
Bass, Danielewicz, Pratt (2000)
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Balance Functions in STAR
 Pairs
• Peripheral collisions approach Hijing (NN)
• Clear narrowing for central collisions
STAR
• In Bass/Danielewicz/Pratt model, central
data consistent with:
Tchem ~ 175 MeV Tkinetic ~ 110 MeV
tchem = 10 fm/c tkinetic = 13 fm/c
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Noncentral collision dynamics
• higher pressure gradient in-plane
 “elliptical flow”
• more particles emitted in-plane
• x-space  p-space anisotropy
Equal energy density lines
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
38
Noncentral collision dynamics
• higher pressure gradient in-plane
 “elliptical flow”
• more particles emitted in-plane
• x-space  p-space anisotropy
• experimentally quantified by v2
dN
~ 1  2v2 cos2f
df
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
39
Noncentral collision dynamics
• higher pressure gradient in-plane
 “elliptical flow”
• more particles emitted in-plane
• x-space  p-space anisotropy
• experimentally quantified by v2
• hydro reproduces v2(pT,m) (details!)
@ RHIC for pT < ~1.5 GeV/c
• system response  EoS
• early thermalization indicated
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Noncentral collision dynamics
• higher pressure gradient in-plane
 “elliptical flow”
• more particles emitted in-plane
• x-space  p-space anisotropy
• experimentally quantified by v2
• hydro reproduces v2(pT,m) (details!)
@ RHIC for pT < ~1.5 GeV/c
• system response  EoS
• early thermalization indicated
v2
0.2
0.1
STAR preliminary
see talk of J. Fu
0
STAR
flow of neutral strange particles
PID beyond pT=1 GeV/c
0
1
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
2
3
pT (GeV/c)
41
Noncentral collision dynamics
• higher pressure gradient in-plane
 “elliptical flow”
• more particles emitted in-plane
• x-space  p-space anisotropy
• experimentally quantified by v2
• hydro reproduces v2(pT,m) (details!)
@ RHIC for pT < ~1.5 GeV/c
• system response  EoS
• early thermalization indicated
v2
0.2
0.1
STAR preliminary
see talk of J. Fu
0
• Again, hydro reproduces p-space
• freezeout shape  evolution duration?
STAR
0
1
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
2
3
pT (GeV/c)
42
Blast-wave fit to low-pT v2(pT,m)
STAR, PRL 87 182301 (2001)
• spatial anisotropy indicated
• consistent with out-of-plane
extended source
(but ambiguity exists)
fp=90°
Rside (small)
• possible to “see” via HBT
relative to reaction plane?
• expect
• large Rside at 0
2nd-order
• small Rside at 90
oscillation
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
Rside (large)
fp=0°
43
Out-of-plane extended source
~ short system evolution time
• Same blastwave parameters as required to
describe v2(pT,m), plus two more:
– Ry = 10 fm  = 2 fm/c
• Both p-space and x-space anisotropies
contribute to R(f)
– mostly x-space: definitely out-of-plane
STAR preliminary
• calibrating with hydro, freezeout ~ 7 fm/c
Ros2 - new “radius” important for
azimuthally asymmetric sources
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
44
Low-pT dynamics — one (naïve?) interpretation:
rapid evolution and a “flash”
RHIC 130 GeV Au+Au
K-
K* yield
Disclaimer:
all numbers (especially
time) are approximate
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
45
Physics at “high” pT (~6 GeV/c)
Jets modified in heavy ion collisions
leading
particle
hadrons
q
-Parton Energy loss in dense nuclear medium
-Modification of fragmentation function
q
hadrons
leading
particle
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Jets in STAR?
OPAL qq jet event
STAR Au+Au event
It’s a little complicated… Need another way to get
at hard scattering physics.
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Physics at “high” pT (~6 GeV/c)
Jets modified in heavy ion collisions
leading
particle
hadrons
q
-Parton Energy loss in dense nuclear medium
q
hadrons
-Modification of fragmentation function
leading
particle
1) high-pT suppression relative to NN
(especially in central collisions)
2) finite, non-hydro v2 due to energy loss
(non-central collisions)
leading
particle
suppressed
hadrons
y
q
q
Jet 2
x
hadrons
leading
particle
suppressed
STAR
see talk of J. Klay
Jet 1
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Inclusive spectra
preliminary
power-law
fits
Statistical errors only
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Power law fits
1 dN
p n
 A(1  )
pT dpT
p0
• Power Law: “pQCD inspired”
• Fits wide range of hadronic spectra: ISR Tevatron
• Good fits at all
centralities (2/ndf~1)
• Smooth dependence on
centrality
STAR preliminary
• most peripheral
converges to NucleonNucleon reference (UA1)
centrality
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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d 2 N AA / dpT d
RAA ( pT ) 
TAAd 2s NN / dpT d
low pT scales as
<Npart>
preliminary
STAR
• Central collisions: suppression of factor 3 (confirms PHENIX)
• Peripheral collisions: “enhancement” consistent with zero
(uncertainties due to <Nbinary> and NN reference)
Warsaw STAR/ALICE
HBT Workshop - May 2002 - malisa
• Smooth transition
central  peripheral
51
Azimuthal anisotropy - theory and data
Low pT: parameterized hydro
High pT: pQCD with GLV radiative energy loss
• finite energy loss  finite v2 at high pT
• sensitive to gluon density
y
Jet 2
Preliminary
x
Jet 1
model: Gyulassy, Vitev and Wang, (2001)
• pT<2 GeV: good description by hydrodynamics
• pT>4 GeV: hydro fails but finite v2
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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V2 centrality dependence
Preliminary
all centralities: finite v2 at high pT
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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But are we looking at jets? - 2 Particle Correlations
• Trigger particle pT>4 GeV/c, ||<0.7
• azimuthal correlations for pT>2 GeV/c
• short range  correlation: jets + elliptic flow
• long range  correlation: elliptic flow
 subtract correlation at |1 2|>0.5
• NB: also eliminates the away-side jet correlations
• extracted v2 consistent with
reaction-plane method
0-11%
preliminary
• what remains has jet-like
structure first indication of jets
at RHIC!
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Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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STAR vs UA1
UA1: Phys. Lett. 118B, 173 (1982)
(most events from high ET trigger data)
preliminary
• UA1: very similar analysis (trigger pT>4 GeV/c)
• But sqrt(s)=540 GeV, ||<3.0
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Brief Summary - (just a small set of STAR results)
• chemistry:
• wide range of particle yields well-described by thermal model
• Tchem ~ 170 MeV mb ~ 45 MeV
• pT dependence of yields (e.g. baryon dominance) consistent with radial flow
• dynamics at pT < 2 GeV/c
• “real” model (hydro) reproduces flow systematics, but not HBT
• finger-physics analysis of probes sensitive to time:
• short system evolution, then emission in a flash
• Tchem ~ 170 MeV
Tkin ~ 110 MeV
• tchem ~ 10 fm/c
tkin ~ 13 fm/c
• naïve? unphysical? useful feedback to modelers?
• dynamics at pT > 2 GeV/c
• hydro picture breaks down
• preliminary jet signal observed
• evidence for medium effects at high pT
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THE END
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Resonance survival rate
kinetic rescattering
d1
d2
R
R
chemical freeze out
T~170 MeV
thermal freeze out
T~110MeV
• short-lived resonances
– K*(892)  = 3.9 fm/c
– L(1520)  = 12.8 fm/c
d1 • Rescattering of daughters
between chemical and kinetic
d2
freeze-out washes out the
time resonance signal
– Sensitive to tkinetic - tchemical
UrQMD: signal loss in invariant mass reconstruction
K*(892) L(1520)
SPS
f
(17 GeV) [1]
66%
50%
26%
RHIC (200GeV) [2]
55%
30%
23%
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Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Resonance reconstruction (via combinatorics):
K* and L(1520) from STAR
K*0 K+ + -
K*0 K- + +
L(1520)  p + K-
minv (GeV/c2)
Upper limit estimation: dN/dy preliminary
multiplicity for |y| <0.5
L(1520) |y|<1 < 1.2 at 95% C. L.
K*0 |y|<0.5 = 10.0 Warsaw
0.8  25%
STAR
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Resonance survival rate:
Rafelski’s picture
• Combining both K* and L(1520):
– D  tkinetic - tchemical ~ 0-3 fm/c
Upper limit
• Caveats:
– partial L “quenching” (width
broadening) allows for higher T,
still small D
– Tchem~100 MeV ?!?
• Thermal fit: T ~ 170 MeV
– no evidence of low-pT suppression
– Possible K* regeneration?
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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pT spectra: Flavor Dependence
Enhancement at ~2 GeV is not
specific to baryons  mass effect
simplest explanation: radial flow)
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A consistent picture within blastwave

pT
 mT
 T sinh r cosfs fp 
coshr e
1
 
f x, p   K1
 T
parameter
Temperature
T  110 MeV
Radial flow
r0  0.6
velocity
Oscillation in ra  0.04
(minbias)
radial flow
Spatial
anisotropy
Radius in y
s2  0.04



y   x / Ry e
2
2 2
spectra

v2(m,pT)

HBT(pT,f)

K-









t 2 / 22
(minbias)
Ry  10-13 fm




(depends on b)
Emission
duration
time delay
STAR
  2 fm/c
<tK>-<t>=0
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa

62
Something different vs pT?
Particle/Antiparticle Ratios
see talk by B. Norman
Within the errors no or very small pT dependence
(as one might expect from simply flow)
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Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Azimuthal variation of transverse flow and source deformation
Consistent values for
source deformation
from HBT and elliptic
flow
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Excitation function of spectral parameters
• Kinetic “temperature” saturates
~ 140 MeV already at AGS
• Explosive radial flow significantly
stronger than at lower energy
• System responds more “stiffly”?
• Expect dominant space-momentum
correlations from flow field
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Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Ratios driving the thermal fits
Plots from D. Magestro, SQM2001
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Blast Wave Mach I - central collisions
bs
s
u (t , r , z  0)  (cosh r , er sinh r , 0)
r  tanh 1 br
R
bt  b s f (r )
Ref. : E.Schnedermann et al, PRC48 (1993) 2462
flow profile selected
2-parameter (Tfo, bt) fit to mT distributions
1/mt dN/dmt
(bt =bs (r/Rmax)n)
bt
A
Tfo
mt
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Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Blastwave Mach II - Including asymmetries
analytic description of freezeout distribution: exploding thermal source
bt
R
 
 mT

f x, p   K1
coshr  
 T

pT
sinh r cosf s  f p 
T
e





 1  y 2  2 x 2 / R y 
STAR
e
 t 2 / D 2
– Flow
• Space-momentum correlations
• <r> = 0.6 (average flow rapidity)
• Assymetry (periph) : ra = 0.05
– Temperature
• T = 110 MeV
– System geometry
• R = 13 fm (central events)
• Assymetry (periph event) s2 =
0.05
– Time: emission duration
• D = emission duration
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Comparison to Hijing
Ratio of integrals over
correlation peak: 1.3
Hijing fragmentation is
independent of quenching
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High-pT highlights
Qualitative change at 2 GeV
Jet-like structure
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Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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measured K- correlations - natural consequence of
space-momentum correlations
• clear space-time asymmetry observed
• C+/C- ratio described by:
– static (no-flow) source w/ tK- t=4 fm/c
– “standard” blastwave w/ no time shift
• We “know” there is radial flow
 further evidence of very rapid freezeout
• Direct proof of radial flow-induced
space-momentum correlations
STAR preliminary
Pion
STAR
<pt>
= 0.12 GeV/c
Kaon
<pt> =STAR/ALICE
0.42 GeV/cHBT Workshop - May 2002 - malisa
Warsaw
71
Vector meson production in Ultra-peripheral collisions
Au
• b > 2R  electromagnetic interactions
• ds/dpT consistent with predictions for
coherent r0 production
g
qq
r0
Au
Signal
region:
pT<0.15 GeV
r0 PT
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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Models to Evaluate Tch and mB
Chemical Freeze-Out Model
Statistical Thermal Model
J.Rafelski PLB(1991)333
J.Sollfrank et al. PRC59(1999)1637
F. Becattini
P. Braun-Munzinger et al. PLB(1999)
Assume: Hadron resonance ideal gas
Assume:
• thermally and chemically equilibrated
fireball at hadro-chemical freeze-out
• law of mass action is applicable !!!
Recipe:
• grand canonical ensemble to
describe partition function  density
of particles of species ri
• fixed by constraints: Volume V, ,
strangeness chemical potential mS,
isospin
• input: measured particle ratios
• output: temperature T and baryochemical potential mB
Particle density of each particle:
Qi
: 1 for u and d, -1 for u and d
: 1 for s, -1 for s
gi
: spin-isospin freedom
mi : particle mass
Tch : Chemical freeze-out
temperature
mq : light-quark chemical potential
ms : strangeness chemical potential
gs : strangeness saturation factor
si
Comparable particle ratios to experimental data
STAR
Warsaw STAR/ALICE HBT Workshop - May 2002 - malisa
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B/B Ratios at RHIC
Ratios calculated for
central events at midrapidity, averaged over
experimental acceptance
in pt.With the assumption
of equal acceptance of
particle and antiparticle
no corrections have to be
applied
STAR preliminary
0.94  0.13
Except:
• Absorption in material
• Production of
secondaries in material
B/B ratios experimentally robust
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