production of hadrons correlated to jets in high energy ...2 outline 1. a brief overview on hadrons...
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Production of Hadrons Correlated to Jets in High Energy Heavy-Ion Collisions
Charles Chiu
Center for Particles and FieldsUniversity of Texas at Austin
ITP-Seminar, Chinese Academy of Science, Beijing, May, 2009
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Outline
1. A brief overview on hadrons production in high energy heavy ion collisions
2. Transverse flow of the Quark-Gluon matter
3. Jet medium interactions4. A model for trigger azimuth dependence
in ridge formation5. Summary
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From Bevalac to RHIC, and to LHCBevalac:U with
2 GeV/N on U-target
AGS-RHIC: Au+Au⌦sNN=200GeV
SPS-LHC: Pb+Pb⌦sNN=5.5TeV
1.Overview on hadron production in heavy ion collisions
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Collaboration
STARSTAR Brazil RussiaUniversidade de Sao Paolo MEPHI – Moscow
LPP/LHE JINR - DubnaChina IHEP-ProtvinoIHEP - BeijingUSTC - HefeiIMP - LanzhouSINR - ShanghaiTsinghua UniversityIPP - Wuhan U.S. Labs
Argonne National LaboratoryEngland Brookhaven National LaboratoryUniversity of Birmingham Lawrence Berkeley National Laboratory
France U.S. UniversitiesIReS 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 collaborators44 institutions9 countries
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Energy range on cosmological scale
6Sorenson, Winterworshop 08
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dσ/dNch vs Nch
Au + Au √sNN = 200 GeV
b
Nch: # of charged pclesin 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
θφ
pT
Pseudorapidity η = ln( cot θ/2 )Transverse mom pT
Azimuthal angle φ
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Is Q-G 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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Inverse slope (“T”) vs MassLight particle: T*=TγT
Massive pcle: mvT
As A increases,
• the slope of the line increases
• collective flow becomes more prominent
PbPb, A=208
SS, A=32,
pp
Shuryak 04
√sNN~25GeV
Evidence on radial flow
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π, K, N Spectra (STAR)
Each Nch-bin is fitted by freeze-out:Tkin & flow speed: β
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) Dilution of nB and of e are due to local expansion
(2) Increase of uµ is due to local pressure gradient
Heinz05, A reviewHydrodynamic-model
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v2 a measure momentum anisotropy
φ
x
y
pp
=φtan
V2 = [ <px2> -<py
2>] / [ <px2> +<py
2>]=< cos2φ >,
dN/dφ = dN/dφ(0o)[ 1 + V2 cos2φ+ …]
Spatial anisotropy momentum anisotropy
y
x x
y
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Elliptic Flow
Equal energy density lines
Kolb, Sollfrank, Heinz
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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 : |η| < 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
ησηddpdTddpNdpRT
NNAA
TAA
TAA //)( 2
2
=
Nuclear Mod. factor
Large pTsuppression
3. Jets-medium interactions
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Ridge phenomena
Two particle correlation STAR: data Putschke, QM06
Central: 3 < pTtrig< 4 GeV, pTassoc > 2 GeV
dN/d∆η vs ∆η
R: Plateau, J: Peak
∆η=ηtrig-ηassoc
∆φ=φtrig-φassoc
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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)
ΦΦ
φ
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 dependenceFeng, STAR (QM08)
3 < pTtrig< 4 GeV; 1.5 < pTassoc< 2 GeVφs
Trigger
Assoc
φ
x
y
Beam
Feature: For 20-60% the yield decreases rapidly with φs.
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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.
• Soft radiation: 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)
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Trigger direction vs flow direction
Mismatched case|φs – ψ|~900 : Enhanced thermal partons dispersed over a wide range of φ -- weak ridge.Local flow along ψ (green)
Trigger along φs (red)
x
Matched case |φs –ψ|~0: Enhanced thermal partons flow in the same direction, leading to strong ridge.
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Ridge yield at φ with trigger φs 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.
φs
(x0,y0)t
Interaction at one point: (x0, y0)
ψφs
φt’
ψC Γ
t’
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Comparison with the data
Parameters:
• Thickness of interaction layer is ~ RA/4
• Gaussian-width of φs−ψ cone ~200.
Normallized to fit one point at lowest φs for 0-5%.
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CEM fit to the φs data
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Comparison with ∆φ data in 20-60% region
Left panel Shift of the peak from ∆φ=0:
• Matched “In”-region (∆φ<0) is larger at ~40%
• Mismatched “out”-region (∆φ>0) is smaller at ~40%
shift
b=0 ~40%
in
out
∆φ= φ -φs
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Model predictions
∆φ curves: The left-shift in the peak position as a function of φs.
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Asymmetry vs φs
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R-yield vs b (or Npart) at various φs
We predict decrease of yield/trigger as b is decreased at small φs
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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 Ridge particle direction and the local flow direction.
– Phenomenological application and further test of the model are presented.
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