Recent results from STAR
M.A. Lisa, for the STAR Collaboration
STAR
APS Spring Meeting - April 2002 - malisa
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Outline
Year-1 data (Au+Au s=130 GeV)
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
elliptical flow
two-particle correlations
• Summary
STAR
APS Spring Meeting - April 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  + 
STAR
K+ K- pairs
APS Spring Meeting - April 2002 - malisa
m 3inv
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
APS Spring Meeting - April 2002 - malisa
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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
APS Spring Meeting - April 2002 - malisa
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Statistical Thermal Model: Fit Results
• b driven by p/p, K-/K+
• T driven by p/
STAR
APS Spring Meeting - April 2002 - malisa
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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)
STAR
APS Spring Meeting - April 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)
STAR
APS Spring Meeting - April 2002 - malisa
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Thermal motion superimposed on radial flow
Hydro-inspired “blast-wave”
thermal freeze-out fits to , K, p, L
preliminary
Tth = 107 ± 8 MeV
hydro predictions reproduce early
pT spectra
Fits by M. Kaneta
STAR
APS Spring Meeting - April 2002 - malisa
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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 flow
Rside
STAR
• Right dynamic effect / wrong space-time
evolution???
 the “RHIC HBT Puzzle”
APS Spring Meeting - April 2002 - malisa
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Blastwave: radii vs pT
Magnitude of 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  2 t2
blastwave: R=13.5 fm,
tfreezeout=1.5 fm/c
K
pT=0.4
STAR
APS Spring Meeting - April 2002 - malisa
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From Rlong: tkinetic = 8-10 fm/c
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
APS Spring Meeting - April 2002 - malisa
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Kaon – pion correlation:
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
STAR
APS Spring Meeting - April 2002 - malisa
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Initial idea: probing emission-time ordering
purple K emitted first
green  is faster
• Catching up: cosY  0
•
•
• Moving away: cosY  0
purple K emitted first
green  is slower
•
•
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
APS Spring Meeting - April 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:
– “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> = APS
0.42Spring
GeV/c
Meeting - April 2002 - malisa
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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
APS Spring Meeting - April 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
APS Spring Meeting - April 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
APS Spring Meeting - April 2002 - malisa
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Noncentral collision dynamics
hydro evolution
• hydro reproduces v2(pT,m) @ RHIC
for pT < ~1.5 GeV/c
• system response (pressure):
x-space  p-space anisotropy
v2
0.2
• again: correct p-space dynamical effect 0.1
• freezeout shape  evolution duration?
STAR preliminary
see talk of J. Fu
0
flow of neutral strange particles
PID beyond pT=1 GeV/c
STAR
0
1
APS Spring Meeting - April 2002 - malisa
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3
pT (GeV/c)
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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
APS Spring Meeting - April 2002 - malisa
Rside (large)
fp=0°
20
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 t = 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, tfreezeout ~ 7 fm/c
Ros2 - new “radius” important for
azimuthally asymmetric sources
STAR
APS Spring Meeting - April 2002 - malisa
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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
APS Spring Meeting - April 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
APS Spring Meeting - April 2002 - malisa
Jet 1
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Inclusive spectra
preliminary
Statistical errors only
STAR
APS Spring Meeting - April 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)
(p0, n highly correlated)
STAR
APS Spring Meeting - April 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)
APS Spring
- April 2002 - malisa
• Smooth transition central
 Meeting
peripheral
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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
APS Spring Meeting - April 2002 - malisa
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V2 centrality dependence
Preliminary
all centralities: finite v2 at high pT
STAR
APS Spring Meeting - April 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!
STAR
APS Spring Meeting - April 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
STAR
APS Spring Meeting - April 2002 - malisa
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Brief Summary
• chemistry:
• wide range of particle yields well-described by thermal model
• Tchem ~ 170 MeV b ~ 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
STAR
APS Spring Meeting - April 2002 - malisa
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THE END
STAR
APS Spring Meeting - April 2002 - malisa
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Ratios driving the thermal fits
Plots from D. Magestro, SQM2001
STAR
APS Spring Meeting - April 2002 - malisa
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Blast Wave Mach I - central collisions
s
s
u (t , r , z  0)  (cosh r , er sinh r , 0)
r  tanh 1 r
R
t   s f (r )
Ref. : E.Schnedermann et al, PRC48 (1993) 2462
flow profile selected
2-parameter (Tfo, t) fit to mT distributions
1/mt dN/dmt
(t =s (r/Rmax)n)
t
A
Tfo
mt
STAR
APS Spring Meeting - April 2002 - malisa
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Blastwave Mach II - Including asymmetries
analytic description of freezeout distribution: exploding thermal source
t
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 / Dt 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
• Dt = emission duration
APS Spring Meeting - April 2002 - malisa
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Comparison to Hijing
Ratio of integrals over
correlation peak: 1.3
Hijing fragmentation is
independent of quenching
STAR
APS Spring Meeting - April 2002 - malisa
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High-pT highlights
Qualitative change at 2 GeV
Jet-like structure
STAR
APS Spring Meeting - April 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> = APS
0.42Spring
GeV/c
Meeting - April 2002 - malisa
38