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K/ π Ratios as Hard Probe in RHIC/LHC PowerPoint PPT Presentation

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K/ π Ratios as Hard Probe in RHIC/LHC. 张一 上海师范大学物理系. Outline. “Little Bang”: RHIC Establishment RHIC – The most recent results The phase diagram of QCD Hard Probes in RHIC: Basics of perturbative QCD (pQCD) Hard particle productions in p-p, p-A and A-A collisions

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K/ π Ratios as Hard Probe in RHIC/LHC

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as Hard Probe in





  • “Little Bang”: RHIC Establishment

    RHIC – The most recent results

    The phase diagram of QCD

  • Hard Probes in RHIC:

    Basics ofperturbative QCD (pQCD)

    Hard particle productions in p-p, p-A and A-A


    K/πratios as hard probe in RHIC (LHC)

  • Conclusions/Outlook

Big Bang




Quark-Gluon Plasma













Hadron Gas

Color Superconductor







E. Shuryak, et. al. Phys.Rev.Lett. 81 (1998)

T. D. Lee, C.G.Wick, Phys.Rev.D 9 (1974)

The Relativistic Heavy Ion Collider


Di-hadron Correlations

Trigger on high pT and

measure the associated hadron

Fragments at time scales

J.Adams et al., Phys.Rev.Lett.91 (2003)

The Ridge from RHIC



Bulk Medium

STAR: Joern Putschke, J.Phys.G34: S679 (2007)

Rich underlying physics: jets, bulk, jet-medium interaction,

medium responses,…

pT and Centrality:π0 Spectra in Au+Au @ sNN = 200 GeV

  • π0 RAA now measured up to pT = 20 GeV/c (central Au+Au)

  • Constant RAA 0.2 in central Au+Au up to highest pT (5 < pT < 20 GeV/c)

PHENIX, arXiv:0801.4020 [nucl-ex]

pT and Centrality:π0 Spectra in Cu+Cu @ sNN = 200 GeV

Cu+Cu, 200 GeV, 60-94%


PHENIX, arXiv:0801.4555 [nucl-ex]

Cu+Cu, 200 GeV, 0-10%

p0 RAA 0.6 – 0.7 in central Cu+Cu collisions at 200 GeV

Hard Probes: Introduction

Hard probes(of the medium created in RHIC): those whose benchmark (result of the probe in cold nuclear matter) can be studied using pQCD, for which a hard scale is required(p_T, Q,...>>1/Rh).


QCD Probes in

QCD Probes Out

Strategy: results with no medium (pp) and cold nuclear matter

effects (pA) understood in pQCD define the benchmark for the

probe; results in hot medium (AB) and their difference with defined

expectation provides a (perturbative or non-perturbative)

characterization of the medium

QCD: Factorizationin Hard Processes

  • Asymptotic freedom allows the use of pQCD for processes with a large

  • scale (m, transverse momentum,...) involving the QCD q, g fields.

  • For inclusive processes, factorization (Collins, Soper, Sterman, '85) is

  • the tool which makes it possible to use pQCD for hadronic processes.

QCD: Factorization in Hard Processes


  • Hard scattering elements computable in perturbation theory @ fixed order (LO or NLO), collinear, e.g.,

  • f: PDF, flux of 'initial' partons in the hadron or nucleus (evolution with scale computable in perturbation theory)

  • D: FF, projection of 'final' partons onto the observed particle (evolution with scale computable in perturbation theory)

pQCD: pp Collision



pQCD: pp Collision

  • Interactions among initial partons  Intrinsic k_T

  • Can be measured experimentally

pQCD: Feynman-Field Fragmentation Function

FF parameterizations, (1) BKK(2) KKP(3) Kretzer (4) AKK

pQCD: pp Collision

RHIC Energies

New Parameterization for K?

Feynman-Field FFs:When z  1, D[u-K]/D[u-π]  1-β/βwhere βsome constant

New Kaon FFs (“Z”) based on KKP’s FF (“KKP”):When z  1, D[u-K]/D[u-π]  ½“K” = Kretzer’s FFs

S.Kretzer, PRD. 62, 054001 (2002)

K/π Ratios in pp Collisions

K+/π+ scaling?Y. Zhang, unpublished (2005)More high p_T kaon data needed…

p-A Collisions: Cronin Effect

  • pQCD (LO) for pp +Cronin + Shadowing

  • Cronin effect: nuclear multi-scattering

    increased particle production in 3 GeV < pT < 6 GeV range where

    ”increased” means more particles are produced in pA than expected from

    scaled pp collisions

p-A Collisions: Shadowing

Different shadowing parameterizations: (1) HIJ [S.-Y. Li and X.-N. Wang, PLB527(2002) 85-91](2) EKS[K.J. Eskola, V.J. Kolhinen and C.A. Salgado, Eur. Phys.J., C9 (1999) 61](3) nPDF [M. Hirai, S. Kumano, and T.-H. Nagai, PRC70, (2004) 044905] (4) nDS[D. de Florian, R. Sassot, PRD69, (2004) 074028]

p-A Collisions: Geometry

p-A: Geometry cont’d

A-A Collisions: Jet Tomography

Jet Tomography: jet production and propagation in AA collision (inside hot dense matter) induced gluon radiation in a modified pQCD description

A-A Collisions: Jet Tomography

A-A Collisions: Jet Tomography

Energy loss of jets decreases the momenta of parton c before its fragmentation:

pQCD calculation for A-A collisions: geometrical overlap + shadowing + multi-scattering + jet-quenching + ...

Nuclear modification factor:

Jet Tomography Predictions

I.Vitev., M.Gyulassy, Phys.Rev.Lett. 89 (2002)

A-A Collisions: Jet Tomography



K/πRatios in dA and AA Collisions

  • AuAu: HIJING shadowing, no jet Quenching!

  • is it sensitive to shadowing parameterization?

  • do we expect this from recombination mechanism?

  • jet quenching…LHC energies…NLO…?

Y. Zhang and G. Fai, in preparation, (2008)

Breakdown of (indep.) (pert.)Fragmentation

U.A.Wiedmann, QM’04

Fragmentation vs. Recombination

Open Q: violates entropy conservation?

U.A.Wiedmann, QM’04


  • pQCD parton model + jet quenching

    - Provide powerful tools for RHIC data

    - Suggests energy density at RHIC more than

    100 times cold nuclear matter density

  • K/π ratios displays some “scaling”


  • K/π ratios might be sensitive hard

    probe in RHIC and LHC (in progress)

High p_T Spectra @ RHIC

200 GeV p+p

Gluons vs Quarks

  • q jets or g jets gluon jet contribution to protons is significantly larger than to pions at high pT in p+p collisions at RHIC; pbar/ < 0.1 from quark jet fragmentation at low beam energy .STAR Collaboration, PLB 637, 161 (2006).

  • From Kretzer fragmentation function, the g/q jet contribution is similar to AKK. S. Kretzer, PRD 62, 054001 (2000).

Jet Tomography in Au-Au @ PHENIX

Dh-Df Two-Component Ansatz



3<pt,trigger<4 GeV

pt,assoc.>2 GeV

  • Study near-side yields

  • Study away-side correlated yields and shapes

  • Components

    • near-side jet peak

    • near-side ridge

    • v2 modulated background

Au+Au 0-10%


Strategy:Subtract  from  projection: isolate ridge-like correlation

Definition of “ridge yield”:

ridge yield := Jet+Ridge()  Jet()

Can also subtract large .

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