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K/ π Ratios as Hard Probe in RHIC/LHC

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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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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)

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
The Ridge from RHIC



Bulk Medium

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

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

medium responses,…

p t and centrality 0 spectra in au au @ s nn 200 gev
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]

p t and centrality 0 spectra in cu cu @ s nn 200 gev
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: 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

q c d factorization in hard processes
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.
q c d factorization in hard processes1
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)
pq c d pp collision1
pQCD: pp Collision
  • Interactions among initial partons  Intrinsic k_T
  • Can be measured experimentally
pq c d feynman field fragmentation function
pQCD: Feynman-Field Fragmentation Function

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

pq c d pp collision2
pQCD: pp Collision

RHIC Energies

new parameterization for k
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 ratios in pp collisions
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
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
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]

a a collisions jet tomography
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 tomography2
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)

k ratios in da and aa collisions
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)

fragmentation vs recombination
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)

gluons vs quarks
200 GeV p+pGluons 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).
dh df two component ansatz
Dh-Df Two-Component Ansatz




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 .