K/K/ππRatiosRatiosas 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 K/πratios as hard probe in RHIC (LHC)

• Conclusions/Outlook

0 200 400 600

100

200

300

0

Big Bang

LHC

RHIC

SPS

Quark-Gluon Plasma

Color SuperconductorHadron Gas

Chiral

symmetry breaking

Quark pairing

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

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

ChandraX-ray

CERN-SPS

0, 0

0, 0 0, 0

T (MeV)

μ(MeV)

The Relativistic Heavy Ion Collider

RHIC 5-YEAR RUNNING

Di-hadron Correlations

1 2

2

1 h h

trig

dNC

N d

Trigger on high pT and measure the associated hadron

Fragments at time scales

K

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

The Ridge from RHIC

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

RidgeJet

Bulk Medium

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

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

0

Cu+Cu, 200 GeV, 60-94%

Cu+Cu, 200 GeV, 0-10%

PH

EN

IX,

arX

iv:0

801

.455

5 [n

ucl

-ex

]

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).

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

QGP?QCD Probes in

QCD Probes Out

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

Remarks:• 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)

20

2 20

1 1

120 , 0.5

gdN

R dy

R fm fm

A-A Collisions: Jet Tomography

STAR

PHENIX

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

U.A.Wiedmann, QM’04Open Q: violates entropy conservation?

Conclusions 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” property K/π ratios might be sensitive hard probe in RHIC and LHC (in progress)

High p_T Spectra @ RHIC

Gluons vs Quarks

1. 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).

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

200 GeV p+p

Jet Tomography in Au-Au @ PHENIX

Study near-side yields

Study away-side correlated yields and shapes

Components

near-side jet peak

near-side ridge

v2 modulated background

Strategy:

Subtract from projection: isolate

ridge-like correlation Definition of “ridge yield”: ridge yield := Jet+Ridge() Jet()Can also subtract large .

3<pt,trigger<4 GeV

pt,assoc.>2 GeVAu+Au 0-10%

preliminary

Two-Component Ansatz