Transcript Slide 1

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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1.Overview on hadron production in heavy ion collisions
From Bevalac to RHIC, and to LHC
Bevalac:U with
2 GeV/N on U-target
AGS-RHIC: Au+Au
WNN=200GeV
SPS-LHC: Pb+Pb
WNN=5.5TeV
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STAR
Collaboration
Brazil
Universidade de Sao Paolo
China
IHEP - Beijing
USTC - Hefei
IMP - Lanzhou
SINR - Shanghai
Tsinghua University
IPP - Wuhan
England
University of Birmingham
419 collaborators
44 institutions
9 countries
France
IReS Strasbourg
SUBATECH - Nantes
Germany
MPI – Munich
University of Frankfurt
India
IOP - Bhubaneswar
VECC - Calcutta
Panjab University
University of Rajasthan
Jammu University
IIT - Bombay
Poland
Warsaw University of Technology
Russia
MEPHI – Moscow
LPP/LHE JINR - Dubna
IHEP-Protvino
U.S. Labs
Argonne National Laboratory
Brookhaven National Laboratory
Lawrence Berkeley National Laboratory
U.S. Universities
UC Berkeley / SSL
UC Davis
UC Los Angeles
Carnegie Mellon University
Creighton University
Indiana University
Kent State University
Michigan State University
City College of New York
Ohio State University
Penn. State University
Purdue University
Rice University
University of Texas - Austin
Texas A&M University
University of Washington
Wayne State University
Yale University
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Energy range on
cosmological scale
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Sorenson, Winterworshop 08
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d/dNch vs Nch
Au + Au sNN = 200 GeV
Nch: # of charged pcles
in an event
b: Distance between 2
centers
Npart: # of participating
NN pairs
“Centrality”: Area-bins
from right to left.
b
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Outgoing particle: Kinematic labels
pT
y
q
f
x
Pseudorapidity  = ln( cot q/2 )
Transverse mom pT
Azimuthal angle f
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2. Transverse flow of the Quark-Gluon matter
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 macrosystem of its own. Expect a collective behavior
following up the explosion.
• Observation of transverse flow signals that the macrosystem has been formed.
– radial flow
– elliptic flow
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Evidence on radial flow
pT-distribution: ~exp[-pT/T*]
Shuryak 04
Light pcle: T*=TgT
PbPb, A=208
T*
sNN~25GeV
Massive: T*~mvT
As A increases,
SS, A=32,
pp
• the line becomes
steeper
• collective flow
becomes more
pronounced
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Blast Wave Model
AA-collision
Central
Intermediate
Peripheral
pp-collision
p, K, N Spectra (STAR)
Each Nch-bin is fitted by
freeze-out:Tkin & flow speed: b
In the central region collective
flow speed reaches 0.6.
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Hydrodynamic-model
Heinz05, A review
Relativistic hydro-equations of ideal fluid
Conserv. of local baryon number, energy and momentum
, 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
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v2 a measure momentum anisotropy
V2 = [ <px2> -<py2>] / [ <px2> +<py2>]=< cos2f >,
dN/df = dN/df(0o)[ 1 + V2 cos2f+
…]
y
y
f
x
t anf 
Spatial anisotropy
x
py
px
momentum anisotropy
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Elliptic Flow
Kolb, Sollfrank, Heinz
Equal energy density lines
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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
midrapidity : || < 1.0
STAR PRL87 (2001)182301
STAR
Model
PRL 86 (2001) 402
Peripheral  Central
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.
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3. Jets-medium interactions
Jet quenching
Nuclear Mod. factor
Large pT
suppression
d 2 N AA / dpT d
RAA ( pT ) 
TAAd 2 NN / dpT d
is highly suppressed
in Au+Au vs in d+Au.
Suppression extends
to all accessible pT.
Away side jet:
Suppressed in Au+Au
Trigger
x
Away-side jet suppressed
Presence in p+p and
in d+Au.
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Ridge phenomena: 2-particle correlation
STAR data. Putschke, QM06
dN/dD vs D
R: Plateau, J: Peak
Differences:
trig. and assoc
Dtrig-assoc
Dfftrig-fassoc
Central: 3 < pTtrig< 4 GeV, pTassoc > 2 GeV
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A ridge model without early therm equilib.
Hwa 08
CC, Hwa, Yang 08
• 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:
F
F
v2(pT,b) is determined based on
phenomenological properties of B(pT) and R(pT)
f
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Comparison between the ridge model and the v2 data
Recombination model: ET up to 5 GeV.
Pions: Include TT, TS, SS
Protons: TTT, TTS, TSS
V2: Pions
V2: Protons
ET<1, TT only.
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Trigger Azimuth dependence
Feng, STAR (QM08)
Feature:
For 20-60% the yield
decreases rapidly
with fs.
y
Assoc
f
3 < pTtrig< 4 GeV; 1.5 < pTassoc< 2 GeV
Beam
Trigger
fs
x
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4. Correlated emission model (CEM)
CC, Hwa 09
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.
y
trigger
x
P(x0,y0)
x
flow
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Trigger direction vs flow direction
Matched case |fs –y|~0:
Enhanced thermal partons
flow in the same direction,
leading to strong ridge.
x
Local flow along y (green)
Mismatched case
|fs – y|~900 : Enhanced
thermal partons dispersed
over a wide range of f
- weak ridge.
Trigger along fs (red)
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Ridge yield per trigger (including all pts)
fs
(x0,y0)
t
Interaction at one point: (x0, y0)
• P(x0, y0, t): Probability parton traverses t and emerges as a trigger.
• Ridge yield at f with trigger fs due to interaction at x0,y0
C
y
t’
f
G
fs
y
t’
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Comparison with the data
CEM fit to the fs data
Parameters:
• Thickness of interaction
layer is ~ RA/4
• Gaussian-width of
fs-y cone ~200.
Normallized to fit one point at lowest fs for 0-5%.
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Comparison with Df data in 20-60% region
Left panel Shift of
the peak from Df=0:
b=0
~40%
out
in
• Matched “In”region (Df<0) is
larger at ~40%
shift
Df= f -fs
• Mismatched “out”region (Df>0) is
smaller at ~40% 26
Model predictions
Df curves: The left-shift in the
Asymmetry vs fs
peak position as a function of fs.
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R-yield vs b (or Npart) at various fs
We predict decrease
of yield/trigger as b is
decreased at small fs
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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.
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