On the Trail of a Dense Plasma at RHIC
(a detector builder’s point of view)
Jim Thomas
Lawrence Berkeley Laboratory
Cornell University Journal Club
5/21/2004
Jim Thomas - LBL
1
The Phase Diagram for Nuclear Matter
K. Rajagopol
The goal is to explore nuclear matter under extreme
conditions – T > mpc2 and r > 10 * r0
Jim Thomas - LBL
•
One of the
goals of RHIC is
to understand
the QCD in the
context of the
many body
problem
•
Another goal is
to discover and
characterize the
Quark Gluon
Plasma
•
RHIC is a
place where
fundamental
theory and
experiment can
meet after many
years of being
apart
2
QCD is a Rich Theory with Many Features
1 ~  a
LHadron
 i D
 diagram
Fa F   Mˆ 
'level'
4
We have a theory of the strong
interaction
Hadron “level” Diagram
1500
Low(er) energy nuclear physics
uses OPEP or descriptions in
terms of a pion gas. These
worked because QCD is a
theory with a mass gap.
This gap is a
manifestation of
the approximate
SU(2)R x SU(2)L
chiral symmetry of QCD
with pions as the
Nambu-Goldstone bosons
1000
Mass
(MeV)
{
r,w
fo
h
500
K
p
W. Zajc
0
0
Jim Thomas - LBL
10
20
Degeneracy
30
40
3
Lattice QCD predictions
Energy Density
Stephan
Boltzman
limits for a
free Quark
Gluon gas
TC ~ 170 15 MeV
eC ~ 0.7 GeV/fm3
e0 ~ 0.16 GeV/fm3
Karsch QM2004
Temperature
TC ~ 170 MeV, a very stable prediction over time & technologies
(F. Karsch, hep-lat/0106019, edited by JT)
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4
Who is RHIC and What Does He Do?
BRAHMS
PHOBOS
PHENIX
h
STAR
RHIC
•
Two independent
rings
•
3.83 km in
circumference
•
Accelerates
everything, from
p to Au
L
p-p
500 1032
Au-Au 200 1026
s
(GeV and cm-2 s-1)
Jim Thomas - LBL
•
Polarized protons
•
Two Large and
two small
detectors have
been built
5
RHIC Physics is Relativistic Nuclear Physics
Jim Thomas - LBL
6
The Initial State is Important
• Only a few of the nucleons
participate as determined by the
impact parameter
• There is multiple scattering in the
initial state before the hard
collisions take place
– Cronin effect
• The initial state is Lorentz
contracted
• Cross-sections become coherent.
– The uncertainty principle allows
wee partons to interact with the
front and back of the nucleus
– The interaction rate for wee partons
saturates ( ρσ = 1 )
• The intial state is even time dilated
– A color glass condensate
Jim Thomas - LBL
• proton • neutron • delta • pion
string
7
How do we ‘see’ RHIC physics?
Time
Projection
Chamber
Magnet
Coils
Silicon
Tracker
SVT & SSD
TPC
Endcap
& MWPC
FTPCs
Beam
Beam
Counters
Endcap
Calorimeter
Central
Trigger
Barrel
& TOF
Barrel EM
Calorimeter
Not Shown: pVPDs,
ZDCs, PMD, and FPDs
4.2 meters
A TPC lies at the heart of STAR
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8
TPC Gas Volume & Electrostatic Field Cage
420 CM
• Gas: P10 ( Ar-CH4 90%-10% ) @ 1 atm
• Voltage : - 28 kV at the central membrane
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135 V/cm over 210 cm drift path
Self supporting Inner Field Cage:
Al on Kapton using Nomex
honeycomb; 0.5% rad length
9
Pixel Readout of a Pad Plane Sector
A cosmic ray + delta electron
3 sigma
threshold
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10
Particle ID
using Topology & Combinatorics
Secondary vertex:
Ks  p + p
Lp +p
X  L+p WL +K
g  e++e-
Ks  p + + p L  p + p-
dn/dm
f  K++Kr  p++pf from K+ K- pairs
background
subtracted
m inv
dn/dm
K+ K- pairs
same event dist.
mixed event dist.
m inv
“kinks”
K  + 
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11
Au on Au Event at CM Energy ~ 130 GeV*A
Data taken June 25, 2000.
The first 12 events were captured on tape!
Real-time track reconstruction
Pictures from Level 3 online
display. ( < 70 mSec )
Jim Thomas - LBL
12
Au on Au Event at CM Energy ~ 130 GeV*A
A Central Event
Typically 1000 to 2000 tracks
per event into the TPC
Two-track separation 2.5 cm
Momentum Resolution < 2%
Space point resolution ~ 500 m
Rapidity coverage –1.8 < h < 1.8
Jim Thomas - LBL
13
Bjorken Estimate of Initial Energy Density
Boost invariant hydrodynamics:
Bjorken Estimate of Initial Energy Density
1 dET
1
3 dN ch
e 2

pT
2
pR  dy pR 
2 dh
Cold nuclear matter:
r0 ~ 0.16 GeV/fm3
e
 4.5 GeV / fm3
e C  0.7 GeV / fm3
~ 6.5 fm

~ 0.2 - 1 fm/c
time to thermalize the
system
30xr0
pR2
nucl-ex/0311017
PRL 87 (01) 52301
dz   0dy
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14
Rapidity vs xf
• xf = pz / pmax
– A natural variable to describe physics at forward scattering angles
• Rapidity is different. It is a measure of velocity but it stretches
the region around v = c to avoid the relativistic scrunch
1  E  pz 

y  ln 
2  E  pz 
or
y  tanh 1 ( pz / E )
β
– Rapidity is relativistically invariant and cross-sections are invariant
dn
dy
y  y  tanh 1 
-6
-4
-2
0
2
4
6
y
Rapidity is the natural kinematic variable for HI collisions
( y is approximately the lab angle where y = 0 at 90 degrees )
Jim Thomas - LBL
15
Identified Particle Spectra at 200 GeV
Bose-Einstein fits
A /( e
m / Teff
mt exponential fits
 1)
p+
Ae
 m / Tm
K-
p+, p-, K+, K- spectra versus centrality
PRL 92 (2004) 171801 and nucl-ex/0206008
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16
Anti-Proton Spectra at 200 & 130 GeV / N
Au + Au  p + X
p
200 GeV data
gaussian fits
Ae p / 2
2
p
2
130 GeV data
p andp spectra versus centrality
PRL 92 (2004) 171801 and PRL 87 (2001) 262302
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17
Anti-Baryon/Baryon Ratios versus sNN
•
In the early universe
–
p / p ratio = 0.999999
•
At RHIC, pair-production
increases with s
•
Mid-rapidity region is not yet
baryon-free!
Ypbar
Ypair

 0.8
Yp
Ypair  YTrans
•
Pair production is larger
than baryon transport
Ypair
 4
YTr
In HI collisions at RHIC, more baryons are
pair produced than are brought in by the
initial state
Jim Thomas - LBL
•
80% of protons from pair
production
•
20% from initial baryon
number transported over 5
units of rapidity
18
Anti-Particle to Particle Ratios
K+/K- ratios

p/p ratios
STAR results on thep/p ratio
• p/p = 0.11 ± 0.01 @ 20 GeV
• p/p = 0.71 ± 0.05 @ 130 GeV
• p/p = 0.80 ± 0.05 @ 200 GeV
Jim Thomas - LBL
Excellent agreement between
experiments at y = 0, s = 130
19
Chemical Freeze-out – from a thermal model
Thermal model fits
Tch (RHIC)  177  7 MeV
μB (RHIC)  29  6 MeV
Tch (SPS)  160  170 MeV
μB (SPS)  270 MeV
Compare to QCD on
Lattice:
Tc = 154 ± 8 MeV (Nf=3)
Tc = 173 ± 8 MeV (Nf=2)
(ref. Karsch QM01)
• The model assumes a thermally and chemically equilibrated fireball at
hadro-chemical freeze-out
• Works great, but there is not word of QCD in the analysis. Done entirely in a
color neutral Hadronic basis!
input: measured particle ratios output: temperature T and baryo-chemical potential
B
20
Jim Thomas - LBL
Putting RHIC on the Phase Diagram
•
Final-state analysis
suggests RHIC reaches
the phase boundary
•
Hadron spectra cannot
probe higher
temperatures
•
Hadron resonance ideal
gas (M. Kaneta and N. Xu,
Lattice results
nucl-ex/0104021 & QM02)
– TCH = 175 ± 10 MeV
– B = 40 ± 10 MeV
Neutron STAR
•
<E>/N ~ 1 GeV
(J. Cleymans and K. Redlich,
PRL 81, p. 5284, 1998 )
We know where we are on the phase diagram but now
we want to know what other features are on the
diagram
Jim Thomas - LBL
21
Kinetic
freeze-out
time
Chemical and Kinetic Freeze-out
Chemical
freeze-out
elastic
interactions
inelastic
interactions
blue beam
• Chemical freeze-out (first)
– End of inelastic interactions
– Number of each particle species
is frozen
• Useful data
– Particle ratios
Jim Thomas - LBL
yellow beam
•
space
Kinetic freeze-out (later)
– End of elastic interactions
– Particle momenta are frozen
•
Useful data
– Transverse momentum distributions
– and Effective temperatures
22
Transverse Flow
Au+Au at 200 GeV
pT ≈ 215 MeV
Kp
T ≈ 310 MeV
T ≈ 575 MeV
The transverse radial expansion
of the source (flow) adds kinetic
energy to the particle distribution.
So the classical expression for
ETot
suggests a linear relationship
Slopes decrease with mass.
<pT> and the effective
temperature increase with mass.
Jim Thomas - LBL
TObs  TKFO  mass   2
23
STAR
Tth [GeV]
STAR Preliminary
PHENIX
<r> [c]
Kinetic Freezeout from Transverse Flow
<ßr> (RHIC) = 0.55 ± 0.1 c
TKFO (RHIC) = 100 ± 10 MeV
Thermal freeze-out determinations are done
with the blast-wave model to find <pT>
Explosive Transverse Expansion at RHIC  High Pressure
Jim Thomas - LBL
24
Anisotropic (Elliptic) Transverse Flow
Peripheral Collisions
z
y
• The overlap region in peripheral collisions
is not symmetric in coordinate space
– Almond shaped overlap region
• Easier for particles to emerge in the
direction of x-z plane
• Larger area shines to the side
– Spatial anisotropy  Momentum anisotropy
• Interactions among constituents
generates a pressure gradient which
transforms the initial spatial anisotropy
into the observed momentum anisotropy
x
Anisotropic Flow
• Perform a Fourier decomposition of the
momentum space particle distributions in
the x-y plane
– v2 is the 2nd harmonic Fourier coefficient of
the distribution of particles with respect to
the reaction plane
1  2 v1 cos(f )  2 v2 cos(2f )  ...
Jim Thomas - LBL
v2  cos 2f
f  atan
py
px
25
v2 vs. Centrality
• v2 is large
Hydro predictions
– 6% in peripheral
collisions
– Smaller for central
collisions
• Hydro calculations
are in reasonable
agreement with the
data
– In contrast to lower
collision energies
where hydro overpredicts anisotropic
flow
PRL 86, (2001) 402
more central 
Anisotropic transverse flow is large at RHIC
Jim Thomas - LBL
• Anisotropic flow
is developed by
rescattering
– Data suggests early
time history
– Quenched at later
times
26
v2 vs. pT and Particle Mass
• The mass dependence
is reproduced by
hydrodynamic models
– Hydro assumes local
thermal equilibrium
– At early times
– Followed by
hydrodynamic
expansion
PRL 86, 402 (2001) & nucl-ex/0107003
Hydro does a surprisingly good job!
Jim Thomas - LBL
D. Teaney et al., QM2001 Proc.
P. Huovinen et al., nucl-th/0104020
27
V2 at high Pt shows meson / baryon differences
Bulk PQCD Hydro
Jim Thomas - LBL
Asym. pQCD Jet Quenching
qn Coalescence
28
The Recombination Model
( Fries et al. PRL 90 (2003) 202303 )
The flow pattern in v2(pT) for hadrons
is predicted to be simple if flow is
developed at the quark level
pT → pT /n
v2 → v2 / n ,
n = (2, 3) for (meson, baryon)
Jim Thomas - LBL
29
What does this mean?
• Hadrons are created by the recombination of quarks and
this appears be the dominant mechanism for hadron
formation at intermediate PT
• Baryons and Mesons are produced with equal abundance at
intermediate PT
• The collective flow pattern of the hadrons appears to reflect
the collective flow of the constituent quarks.
Partonic Collectivity
Jim Thomas - LBL
30
Lets look at some collision systems in detail …
Initial state
Final state
Au + Au
d + Au
p + p
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31
Partonic energy loss via leading hadrons
Energy loss 
softening of fragmentation 
suppression of leading hadron yield
d 2 N AA / dpT dh
RAA ( pT ) 
TAAd 2 NN / dpT dh
Jim Thomas - LBL
Binary collision scaling
p+p reference
32
Au+Au and p+p: inclusive charged hadrons
PRL 89, 202301
nucl-ex/0305015, PRL in press
p+p reference spectrum measured at RHIC
Jim Thomas - LBL
33
Suppresion of inclusive hadron yield
RAA
Au+Au relative to p+p
RCP Au+Au central/peripheral
nucl-ex/0305015
• central Au+Au collisions: factor ~4-5 suppression
Jim Thomas - LBL
• pT>5 GeV/c: suppression ~ independent of pT
34
PHENIX observes a similar effect (p0s)
nucl-ex/0304022
lower energy
Pb+Pb
lower energy
aa
Factor ~5 suppression for
central Au+Au collisions
Jim Thomas - LBL
35
The Suppression occurs in Au-Au but not d-Au
Jim Thomas - LBL
36
Jet Physics … it is easier to find one in e+eJet event in ee collision
Jim Thomas - LBL
STAR Au+Au collision
37
Identifying jets on a statistical basis in Au-Au
•
You can see the jets in p-p data at
RHIC
•
•
Identify jets on a statistical basis in Au-Au
Given a trigger particle with pT > pT (trigger),
associate particles with pT > pT (associated)
C2 (f , h ) 
Jim Thomas - LBL
1
NTRIGGER
1
N (f , h )
Efficiency
STAR Data
Au+Au @ 200 GeV/c
0-5% most central
4 < pT(trig) < 6 GeV/c
2 < pT(assoc.) < pT(trig)
38
Angular Distribution:
Peripheral Au+Au data vs. pp+flow
C2 (Au  Au)  C2 ( p  p)  A * (1 2v 22 cos(2f ))
Ansatz:
A high pT
triggered
Au+Au event is a
superposition of
a high pT
triggered
p+p event plus
anisotropic
transverse flow
v2 from reaction
plane analysis
“A” is fit in nonjet region
(0.75<|f|<2.24)
Jim Thomas - LBL
39
Angular Distribution:
Central Au+Au data vs. pp+flow
C2 (Au  Au)  C2 ( p  p)  A * (1 2v 22 cos(2f ))
Jim Thomas - LBL
40
j correlations vs the reaction plane
p/4
Out-of-plane
3p/4
pTtrigger=4-6 GeV/c, 2<pTassociated<pTtrigger, |h|<1
y
x
in-plane
-3p/4
-p/4
Back-to-back suppression out-of-plane stronger than in-plane
Effect of path length on suppression is experimentally accessible
Jim Thomas - LBL
41
What does it mean?
•
•
•
The backward going jet is missing in
central Au-Au collisions when compared to
p-p data + flow
The backward going jet is not suppressed
in d-Au collisions
Surface emission
These data suggest opaque nuclear matter
and surface emission of jets
Jim Thomas - LBL
Suppression of back-to-back correlations in central Au+Au collisions
42
Exp: Conclusions About Nuclear Matter at RHIC
• Its hot
– Chemical freeze out at 175 MeV
– Thermal freeze out at 100 MeV
– The universal freeze out temperatures are surprisingly flat as a function of s
• Its fast
– Transverse expansion with an average velocity greater than 0.55 c
– Large amounts of anisotropic flow (v2) suggest hydrodynamic expansion
and high pressure at early times in the collision history
• Its opaque
– Saturation of v2 at high pT
– Suppression of high pT particle yields relative to p-p
– Suppression of the away side jet
• And its not inconsistent with thermal equilibrium
– Excellent fits to particle ratio data with equilibrium thermal models
– Excellent fits to flow data with hydrodynamic models that assume
equilibrated systems
Jim Thomas - LBL
43
‘They say …’
• ‘Some theorists say’ we have discovered the Quark Gluon
Plasma at RHIC
– Evidence for PQCD via vn bulk collective flow of 104 p, K,p,L, X, W
– Evidence for pQCD jet quenching in Au+Au at RHIC
– Evidence jet un-quenching in D+Au = Null Control
• The experimental community is somewhat more cautious
because, in part, its not clear what the words mean
– Web definition for plasma: A low-density gas in which the
individual atoms are charged, even though the total number of
positive and negative charges is equal, maintaining an overall
electrical neutrality.
– In the collision of two heavy ions, we have found a high density
plasma containing quarks and gluons.
So whats the problem with the experimentalists?
Jim Thomas - LBL
44
Are the theories a unique explanation for the data?
Jim Thomas - LBL
45
Au+Au Datasets
Au Events
120
Million Events
100
80
d+Au
AuAu 62 GeV
60
AuAu 130 GeV
AuAu 200 GeV
40
20
0
2000
2001
2002
2004
Year
 This year: extremely successful run, all goals met
 Greater than order of magnitude increase in dataset
Jim Thomas - LBL
46
Rcp ratios
At h =0 the
central events
have the ratio
systematically
above that of
semi-central
events. We see
a reversal of
behavior as we
study events at
h=3.2
Rcp 
Jim Thomas - LBL
1/<Ncoll
central>
1/<Ncoll periph>
NABcentral(pT,h)
NABperiph(pT,h)
47
RdAu ratios
Cronin like
enhancement
at h=0.
Clear
suppression
as h changes
up to 3.2
RdA
2Nd+Au/dp dh
1
d
T

2
pp
<Ncoll> d N inel/dpTdh
Same ratio
made with
dn/dh
follows the
low pT RdAu
where < Ncoll> = 7.2±0.3
Jim Thomas - LBL
48
Current State of Affairs
• A theory is something nobody believes, except the person
who made it.
• An experiment is something everybody believes, except the
person who made it.
– attributed to Albert Einstein
Jim Thomas - LBL
49
Recombination Tested
The complicated observed flow pattern in v2(pT)
d2n/dpTdf ~ 1 + 2 v2(pT) cos (2 f)
is predicted to be simple at the quark level under
pT → pT / n , v2 → v2 / n , n = 2,3 for meson,baryon
if the flow pattern is established at the quark level
Compilation
courtesy of H.
Huang
Jim Thomas - LBL
50
Quark Coalescence
 At low pt: mass ordering 
hydrodynamics
 At larger pt: Baryons – mesons
S.A. Voloshin, Nucl. Phys. A715, 379 (2003).
 quark coalescence
Z. Lin et al., Phys. Rev. Lett., 89, 202302 (2002).
 We need v2 of f and r
Jim Thomas - LBL
0
R. Fries et al., nucl-th/0306027.
D. Molnar and S.A. Voloshin, PRL 91, 092301(2003).
51
Multi-Strange Baryons v2
 Multi-strange baryons flow !
Partonic Collectivity !
Jim Thomas - LBL
52
Outer and Inner Sectors of the Pad Plane
•
24 sectors
(12 on a side)
Outer sector
6.2 × 19.5 mm pads
3940 pads
Jim Thomas - LBL
Inner sector
2.85 × 11.5 mm pads
1750 pads
•
Large pads
good dE/dx
resolution in
the Outer
sector
•
Small pads
for good
two track
resolution
in the inner
sector
60 cm
190 cm
53
TPC Sector Detail
•
•
•
Gating Grid
Ground Plane of Wires
Anodes
– No field shaping wires
• Simple and reliable
– Individually terminated anode
wires limit cross-talk
– Low gain
•
Pad Plane
Sector Operation for 20:1 signal to noise
Jim Thomas - LBL
Sector
gas gain
inner
outer
3000
1100
anode
voltage
1150
1380
54
Sector Readout of Pad Planes
Readout arranged like the face of a clock - 5,690 pixels per sector
Jim Thomas - LBL
55
Particle Identification by dE/dx
Anti - 3He
dE/dx PID range:
~ 0.7 GeV/c for K/p
~ 1.0 GeV/c for K/p
Jim Thomas - LBL
56
Summary of Performance Achieved to date
•
Features of the STAR TPC
–
–
–
–
–
–
–
–
–
•
•
4 meters in diameter, 210 cm drift
No field wires in the anode planes
Pad readout, Low gain on anodes
•
Low drift field
Very compact FEE electronics
Analog Delay with SCA then onboard ADC
Data delivered via optic fiber
Uniform E and B fields
‘ExB’ and most Electrostatic distortions
•
correctable to 50 – 100 m level
Position resolution
– 500 m in the real world with calibration
errors
– Space point resolution ~ 100 m for select
laser events, 250 - 350 m for select
tracks
– Function of dip angle and crossing angle
Jim Thomas - LBL
Good particle separation using dE/dx
– 6.5% dE/dx resolution @ 100 cm
– p-proton separation : > 1 GeV/c
2-Track resolution
– 2.5 cm for HBT pairs
– 1.5 cm for laser tracks
– limited by 3 pad response function
and desire for fast algorithms
Momentum resolution
– 2% minimum at 0.25 Tesla (half field)
– for pT > 1.5 GeV in 0.25 T field
• dk/k = 0.016 pT + 0.012 (central)
• dk/k = 0.011 pT + 0.013 (peripheral)
• 2.9%  3.3% peripheral/central
@ 1.5 GeV
STAR performance is excellent
and meets essentially all design
specifications!
57
Something Funny Happens at T > mpc2
An exponentially increasing density of hadronic states suggests
– A “limiting temperature” TH
– A phase transition(?) in hadronic matter
This was noticed before quarks were identified as the constituents of matter
– ( Hagedorn, Nuovo Cimento Supp., 3 (147) 1965 )
Density of States vs Energy
Density of States .vs.
250
Energy
Fit this form
with TH = 163 MeV
r ( m) 
200
dn
~ m a e m / TH
dm
Thermal equilibrium suggests
Number of 150
available
states 100

50
~
m /T
r
(
m
)
e
dm


ma e
m(
1 1
 )
TH T
dm
0
0
Jim Thomas - LBL
500
1000
Mass (MeV)
1500
2000
Which requires T < TH
58
v2: Scaling
 Meson – baryon Effect ?
 Exp. data consistent with quark
recombination/coalescence scenario
 Further tests: f, r0, K*, …
S.A. Voloshin, Nucl. Phys. A715, 379 (2003).
Z. Lin et al., Phys. Rev. Lett., 89, 202302 (2002).
R. Fries et al., nucl-th/0306027.
D. Molnar and S.A. Voloshin, PRL 91, 092301(2003).
Jim Thomas - LBL
59
<pT> Fluctuations → Correlations
 pt  fluctuation inversion
single point
fluctuation scale
dependence  twoparticle correlations
data
statistical
reference
pt fluctuation excess
2D scale inversion
200 GeV Au-Au data
minijet dissipation &
velocity/temperature structure:
f
• elongation on h
h
• necking on f
peripheral
STAR preliminary
central
soft partons as
extended objects
Jim Thomas - LBL
60
Baryon Enhancement
S.S. Adler et al., nucl-ex/0305036.
 Simple fragmentation picture fails for pT less than ~6 GeV/c
p+pbar/h enhancement in Au + Au not fully explained by Cronin effect
 Strong baryon/meson modification in Au + Au also in L/K0s ratio
Jim Thomas - LBL
61
RCP of Strange Hadrons
 Two groups (2<pt<6GeV/c):
- K0s, K, K*, f  mesons
- L, X, W
 baryons
 dependence on number of
valence quarks
 limited to pt<6GeV/c ?
 hadron production from
quark recombination/
coalescence ?
Jim Thomas - LBL
62
Jet Quenching
 Au + Au, RAA << 1; d+Au, RdAu > 1
 p+p, away side jet exists
 Au + Au, away-side correlation suppressed
 d+Au, away-side correlation exists
 jet quenching ?
J. Adams et al., Phys. Rev. Lett. 91, 072304 (2003).
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Hadron suppression @62 GeV
•
•
Significant suppression @62, 130, 200 GeV
Smooth evolution of suppression with energy
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Triggered Correlation Studies
pTrigger = 4 -6GeV/c
STAR Preliminary
STAR Preliminary
 Au+Au: Away-side
 blue band: <pt> in away-side
suppression is larger in the out-
correlation, decreases with centrality
of-plane direction compared to
 solid line: <pt> of bulk, increases with
in-plane
centrality  transverse radial flow
 jet quenching ?
Jim Thomas - LBL
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Anti-Proton to Proton Yields vs. Y
1
0.8
antiproton
to proton
ratio
BRAHMS
0.6
STAR
PHOBOS
0.4
PHENIX
0.2
Points reflected
about y = 0
0
-3
-2
-1
0
1
2
3
y
s = 130 Results
Pbar/ P | Y=0.0 = 0.64  0.04  0.06
Pbar/ P | Y=0.7 = 0.66  0.03  0.06
Evidence for the development of a
(nearly) baryon-free central region
Pbar/ P | Y=2.0 = 0.41  0.04  0.06
BRAHMS PRL 87 No. 11 (2001).
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Part I: full jet reconstruction
in p+p, d+Au
Including EMCal information
ET
ET
Jim Thomas - LBL
A first look…
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