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Production of Hadrons Correlated to Jets in High Energy Heavy-Ion Collisions
Charles Chiu
Center for Particles and Fields
University of Texas at Austin
Shangdong University, Jinan, Shangdong, June 8, 2009
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Outline
1. An overview on hadrons production in high energy heavy ion collisions
2. Transverse flow of the Quark-Gluon matter
3. Jet-medium interactions
4. Ridge phenomena, and the correlated emission model (CEM)
5. Summary
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From Bevalac to RHIC, and to LHCBevalac:U with 2 GeV/N on U-target
AGS-RHIC: Au+Au WNN=200GeV
SPS-LHC: Pb+Pb WNN=5.5TeV
1.Overview on hadron production in heavy ion collisions
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Collaboration
STARSTARBrazil RussiaUniversidade de Sao Paolo MEPHI – Moscow
LPP/LHE JINR - DubnaChina IHEP-Protvino IHEP - BeijingUSTC - Hefei IMP - LanzhouSINR - ShanghaiTsinghua UniversityIPP - Wuhan U.S. Labs
Argonne National LaboratoryEngland Brookhaven National LaboratoryUniversity of Birmingham Lawrence Berkeley National Laboratory
France U.S. Universities IReS Strasbourg UC Berkeley / SSLSUBATECH - Nantes UC Davis
UC Los AngelesGermany Carnegie Mellon UniversityMPI – Munich Creighton UniversityUniversity of Frankfurt Indiana University
Kent State UniversityIndia Michigan State UniversityIOP - Bhubaneswar City College of New YorkVECC - Calcutta Ohio State UniversityPanjab University Penn. State UniversityUniversity of Rajasthan Purdue UniversityJammu University Rice UniversityIIT - Bombay University of Texas - Austin
Texas A&M UniversityPoland University of Washington Warsaw University of Technology Wayne State University
Yale University
419 collaborators 44 institutions 9 countries
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d/dNch vs Nch
Au + Au sNN = 200 GeV
b
Nch: # of charged pcles in an event
b: Distance between 2 centers
Npart: # of participating
NN pairs
“Centrality”: Area-bins from right to left.
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Outgoing particle: Kinematic labels
y
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x
pT
Pseudorapidity = ln( cot /2 )
Transverse mom pT
Azimuthal angle
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Is Quark-Gluon matter really produced in HIC?
• If it is, particles produced should not be incoherent superposition of those from NN collisions.
• The hadronic matter should be regarded as a macro-system of its own. Expect a collective behavior following up the explosion.
• Observation of transverse flow signals that the macro-system has been formed.– radial flow – elliptic flow
2. Transverse flow of the Quark-Gluon matter
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pT-distribution: ~exp[-pT/T*]
Light pcle: T*=TT
Massive: T*~mvT
As A increases,
• the line becomes steeper
• collective flow becomes more pronounced
PbPb, A=208
SS, A=32,
pp
Shuryak 04
sNN~25GeV
Evidence on radial flow
T*
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, K, N Spectra (STAR)
Each Nch-bin is fitted by freeze-out:Tkin & flow speed:
In the central region collective flow speed reaches 0.6.
AA-collision
Central
Intermediate
Peripheral
pp-collision
Blast Wave Model
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Conserv. of local baryon number, energy and momentum
Relativistic hydro-equations of ideal fluid
, leads to ( with )
(1)
(2)
Here cs is the speed of sound, with
(1) Decrease of nB and e due to local expansion
(2) Acceleration is due to local pressure gradient
Heinz05, A reviewHydrodynamic-model
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v2 a measure momentum anisotropy
x
y
p
ptan
V2 = [ <px2> -<py
2>] / [ <px2> +<py
2>]=< cos2 >,
dN/d = dN/d(0o)[ 1 + V2 cos2+ …]
Spatial anisotropy momentum anisotropy
y
x x
y
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Hydro model: pT dependence. Kolb&Rapp03
Model describs pT spectra of various species & centralities
• Decoupling temperature assumed, 165MeV (blue), 100 MeV (red).
• Early thermal equilibrium: t0~0.6 f/c is used.
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Comparison between hydro-model and the v2 data
Centrality dependence:
Overall agreement, except near peripheral region where model prediction v2 is larger than data.
PT-curves for pions and protons are confirmed by the data. More accurate kaon data are needed.
STAR PRL87 (2001)182301midrapidity : || < 1.0
Peripheral Central
STARModel
PRL 86 (2001) 402
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Jet quenching
is highly suppressed in Au+Au vs in d+Au.
Suppression extends to all accessible pT.
Away side jet:
Suppressed in Au+Au
Presence in p+p and in d+Au.x
Trigger
Away-side jet suppressed
ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
Nuclear Mod. factor
Large pT suppression
3. Jets-medium interactions
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Ridge phenomena: 2-particle correlation
STAR data. Putschke, QM06
Central: 3 < pTtrig< 4 GeV, pTassoc > 2 GeV
dN/d vs
R: Plateau, J: Peak
trig-assoc
trig-assoc
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Differences: trig. and assoc
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A ridge model without early therm equilib.
• Assume many semi-hard jets (2-3 GeV) are produced near the surface of the initial almond.
• Jets-medium interaction generates a layer of enhanced thermal partons. They are the ridge particles, R.
• The bulk thermal medium background, B is isotropic. • Total thermal partons yield:
v2(pT,b) is determined based on phenomenological properties of B(pT) and R(pT)
Hwa 08CC, Hwa, Yang 08
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Comparison between the ridge model and the v2 data
Recombination model: ET up to 5 GeV.Pions: Include TT, TS, SSProtons: TTT, TTS, TSS
ET<1, TT only.
V2: Pions V2: Protons
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Trigger Azimuth dependence
Feng, STAR (QM08)
3 < pTtrig< 4 GeV; 1.5 < pTassoc< 2 GeVs
Trigger
Assoc
x
y
Beam
Feature:
For 20-60% the yield decreases rapidly with s.
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A scenario on the ridge formation
• A semi-hard collision at P. One parton exits as trigger, the other absorbed by the medium.
• Exit parton traverses through the medium, accompanied by soft radiations.
• Absorption of radiation energy locally energizes the thermal partons
• Enhanced thermal partons carried by the flow. They lead to the formation of ridge particles.
x
x
y
P(x0,y0)
trigger
flow
4. Correlated emission model (CEM) CC, Hwa 09
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Trigger direction vs flow direction
Mismatched case |s – |~900 : Enhanced thermal partons dispersed over a wide range of -- weak ridge. Local flow along (green)
Trigger along s (red)
x
Matched case |s –|~0: Enhanced thermal partons flow in the same direction, leading to strong ridge.
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• Ridge yield at with trigger s due to interaction at x0,y0
Ridge yield per trigger (including all pts)
• P(x0, y0, t): Probability parton traverses t and emerges as a trigger.
s
(x0,y0)
tInteraction at one point: (x0, y0)
s
t’
C
t’
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Comparison with the data
Parameters:
• Thickness of interaction layer is ~ RA/4
• Gaussian-width of scone ~200.
Normallized to fit one point at lowest s for 0-5%.
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CEM fit to the s data
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Comparison with data in 20-60% region
Left panel Shift of the peak from =0:
• Matched “In”-region (<0) is larger at ~40%
• Mismatched “out”-region ( is smaller at ~40%
shift
b=0 ~40%
in
out
= -s
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Model predictions
curves: The left-shift in the peak position as a function of s.
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Asymmetry vs s
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R-yield vs b (or Npart) at various s
We predict decrease of yield/trigger as b is decreased at small s
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5.Summary
• Some well known features are:– Experimental evidence of transverse collective flows
– Hydrodynamic model has been success in predicting pT spectrum and v2 data at least up to 1GeV
– There are strong jet-medium interactions, and the medium strongly absorptive.
• More recent discovery of Ridge phenomenon is discussed. – Ridge particles are generated in jet-medium interaction.
They are the enhanced thermal partons.
– CEM assumes there is strong correlation between the trigger direction and the flow direction.
– Phenomenological application and further test of the model are presented.