k/ π ratios as hard probe in rhic/lhc
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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