Production of Hadrons Correlated to Jets in High Energy Heavy-Ion Collisions Charles Chiu Center for Particles and Fields University of Texas at Austin ITP-Seminar, Chinese Academy of Science, Beijing, May, 2009 1
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 interactions 4. A model for trigger azimuth dependence in ridge formation 5. Summary 2
1.Overview on hadron production in heavy ion collisions Bevalac:U with 2 GeV/N on U-target From Bevalac to RHIC, and to LHC AGS-RHIC: Au+Au s NN =200GeV SPS-LHC: Pb+Pb s NN =5.5TeV 3
STAR Collaboration 419 collaborators 44 institutions 9 countries Brazil Universidade de Sao Paolo China IHEP - Beijing USTC - Hefei IMP - Lanzhou SINR - Shanghai Tsinghua University IPP - Wuhan England University of Birmingham 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 4
Energy range on cosmological scale 5
Sorenson, Winterworshop 08 6
dσ/dn ch vs N ch Au + Au s NN = 200 GeV Nch: # of charged pcles in an event b: Distance between 2 centers N part : # of participating NN pairs Centrality : Area-bins from right to left. b 7
Outgoing particle: Kinematic labels p T y θ φ x Pseudorapidity η = ln( cot θ/2 ) Transverse mom p T Azimuthal angle φ 8
2. Transverse flow of the Quark-Gluon matter 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 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 9
Evidence on radial flow Inverse slope ( T ) vs Mass Shuryak 04 Light particle: T*=Tγ T s NN ~25GeV PbPb, A=208 SS, A=32, pp Massive pcle: mv T As A increases, the slope of the line increases collective flow becomes more prominent 10
Blast Wave Model AA-collision Central Intermediate Peripheral pp-collision π, K, N Spectra (STAR) Each Nch-bin is fitted by freeze-out:t kin & flow speed: β In the central region collective flow speed reaches 0.6. 11
Hydrodynamic-model Relativistic hydro-equations of ideal fluid Heinz05, A review Conserv. of local baryon number, energy and momentum, leads to ( with ) (1) (2) Here c s is the speed of sound, with (1) Dilution of n B and of e are due to local expansion (2) Increase of u µ is due to local pressure gradient 12
v 2 a measure momentum anisotropy V 2 = [ <p x2 > -<p y2 >] / [ <p x2 > +<p y2 >]=< cos2φ >, dn/dφ = dn/dφ(0 o )[ 1 + V 2 cos2φ+ ] y y x φ x Spatial anisotropy tan φ = p p y x momentum anisotropy 13
Elliptic Flow Kolb, Sollfrank, Heinz Equal energy density lines 14
Hydro model: p T dependence. Kolb&Rapp03 Model describs p T spectra of various species & centralities Decoupling temperature assumed, 165MeV (blue), 100 MeV (red). Early thermal equilibrium: t 0 ~0.6 f/c is used. 15
Comparison between hydro-model and the v 2 data midrapidity : η < 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 v 2 is larger than data. P T -curves for pions and protons are confirmed by the data. More accurate kaon data are needed. 16
3. Jets-medium interactions Jet quenching Large pt suppression Nuclear Mod. factor R AA 2 AA d N / dpt dη ( pt ) = 2 NN T d σ / dp dη AA is highly suppressed in Au+Au vs in d+au. Suppression extends to all accessible p T. T Away side jet: Suppressed in Au+Au Trigger x Presence in p+p and in d+au. Away-side jet suppressed 17
Ridge phenomena Two particle correlation STAR: data Putschke, QM06 dn/d η vs η R: Plateau, J: Peak η=η trig -η assoc φ=φ trig -φ assoc Central: 3 < p Ttrig < 4 GeV, p Tassoc > 2 GeV 18
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: Φ Φ φ v 2 (p T,b) is determined based on phenomenological properties of B(p T ) and R(p T ) 19
Comparison between the ridge model and the v 2 data Recombination model: E T up to 5 GeV. Pions: Include TT, TS, SS Protons: TTT, TTS, TSS V 2 : Pions V 2 : Protons E T <1, TT only. 20
Trigger Azimuth dependence Feng, STAR (QM08) Feature: For 20-60% the yield decreases rapidly with φ s. y Assoc φ Trigger 3 < p Ttrig < 4 GeV; 1.5 < p Tassoc < 2 GeV Beam φ s x 21
4. Correlated emission model (CEM) 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. y x P(x 0,y 0 ) flow trigger x 22
Trigger direction vs flow direction x Matched case φ s ψ ~0: Enhanced thermal partons flow in the same direction, leading to strong ridge. Local flow along ψ (green) Trigger along φ s (red) Mismatched case φ s ψ ~90 0 : Enhanced thermal partons dispersed over a wide range of φ - - weak ridge. 23
Ridge yield per trigger (including all pts) φ s Interaction at one point: (x 0, y 0 ) (x 0,y 0 ) t P(x 0, y 0, t): Probability parton traverses t and emerges as a trigger. Ridge yield at φ with trigger φ s due to interaction at x 0,y 0 t C ψ φ s Γ t φ ψ 24
Comparison with the data CEM fit to the φ s data Parameters: Thickness of interaction layer is ~ R A /4 Gaussian-width of φ s ψ cone ~20 0. Normallized to fit one point at lowest φ s for 0-5%. 25
Comparison with φ data in 20-60% region Left panel Shift of the peak from φ=0: b=0 ~40% out in shift φ= φ -φ s Matched In - region ( φ<0) is larger at ~40% Mismatched out - region ( φ>0) is smaller at ~40% 26
Model predictions φ curves: The left-shift in the peak position as a function of φ s. Asymmetry vs φ s 27
R-yield vs b (or N part ) at various φ s We predict decrease of yield/trigger as b is decreased at small φ s 28
5.Summary Some well known features are: Experimental evidence of transverse collective flows Hydrodynamic model has been success in predicting p T spectrum and v 2 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. 29