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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

8

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.