Momentum Kick Model and the Quenching of Charm Quark

UCLA Jan 22-24, 2009
Momentum Kick Model and the Clustering
of Heavy Quarks in QGP
Cheuk-Yin Wong
Oak Ridge National Laboratory
• Introduction to the momentum kick model for the
near-side ridge
• Successes of momentum kick model for light quarks
• Failures of momentum kick model for heavy quarks
• Clustering phenomenon of slow heavy quarks
• Conclusions
C.Y.Wong, Phy.Rev.C76,054908(’07)
C.Y.Wong, Chinese Phys. Lett.25,3939(08)
C.Y.Wong, J. Phys. G35,104085(08)
C.Y.Wong, Phy.Rev.C78,064905(’08)
C.Y.Wong, arXiv:0901.0726(’09)
C.Y.Wong, Phys. Rev. C76,014902(’07)
1

What is the ridge phenomenon
jet
ridge
• Particles are detected associated with
a near-side trigger
• Δφ=φ (particle)- φ (trigger jet)
Δη=η (particle)- φ (trigger jet)
Δφ
Δη
Find: Δφ- Δη correlation
Probability distribution P(Δφ, Δη ) is in the form of
(i) a “jet component”
(ii) a “ridge component”.
Putschke et al. (STAR) J.Phys..G74 S679(’07)
2

Many Ridge Models
• S.A.Voloshin, Phys. Lett. B632, 490 (`06)
• C.Y.Wong, Phy.Rev.C76,054908(’07);arXiv:0712.3282;arxiv:0806.2154(’08)
• E. Shuryak, C76, 047901 (`07)
• V. S. Pantuev, arxiv:0710.1882
• R.C. Hwa, arXiv:0708.1508
• Nestor Armesto, Carlos A. Salgado, Urs Achim Wiedemann, Phys.
Rev. C 76, 054908 (2007)
• Adrian Dumitru, Yasushi Nara, Bjoern Schenke,
Michael Strickland, arXiv:0710.1223
• A. Majumder, B. Müller, and S. A. Bass, Phys. Rev. Lett. 99,
042301 (2007)
• R. Mizukawa, T. Hirano, M. Isse, Y. Nara, A. Ohnishi,
arXiv:0805.2795
• Sean Gavin, Larry McLerran, George Moschelli, arXiv:0806.4718
• A. Dumitru,F. Gelis, L. McLerran, and R. Venugoplan, arxiv:
0804.3858.
• •••• many more
3

Experimental observations and their implications
• (i) Ridge yield correlated with N_participants
• (ii) Ridge yield nearly independent of pt trigger,
flavor, baryon, light meson characters of the jet
• (iii) Brayon/meson ratios in the ridge and in inclusive bulk are similar
• (iv) T_ridge is similar to T_inclusive but slightly higher
~
→ ridge particles are medium partons
• (v) Δφ ~ 0 implies that the ridge particles acquire their azimuthally
properties from the jet
• (vi) jet-(medium parton) interactions are short-ranged because of
non-perturbative screening
→ ridge particles are medium partons kicked by the jet
and they acquire a momentum kick q along the jet
direction
4

Schematic picture of the momentum kick model
jet
ridge
Δφ
Δη
5

The momentum kick model
6

Momentum kick model described well STAR near-side data
around Δη~0
Data from STAR Collaboration
PRL95,152301(05) & J. Phy. G34, S679 (07)
8

Parton momentum distribution
at the moment of jet-parton collision
9

Ridge yield is a maximum at Δφ~0
10

Momentum kick model described well STAR near-side data
around Δη~0
Data from STAR Collaboration
PRL95,152301(05) & J. Phy. G34, S679 (07)
11

Momentum kick model described well STAR near-side data
around 2.7

Momentum kick model gives the correct prediction
for the PHOBOX data
Data from Wenger et al.(J.Phys.G35,104080(’08)
13

ptrig=2-3GeV
ptrig=3-4GeV
ptrig=4-5GeV
PHENIX Data
ptrig=5-10GeV
14

STAR preliminary heavy quark data
CuCu at sqrt(s)=200 GeV
0.15

STAR preliminary heavy quark data
AuAu at sqrt(s)=200 GeV
0.15

CuCu
PYTHIA results
AuAu
Jet component associated with heavy quark is small.
G.Wang et al. J.Phys. G35, 104107(’08)
18

Momentum kick model fails to reproduce STAR particle
near-side yields associated with heavy quarks
Experimnetal large associated particle yield suggests
collective medium excitation by heavy quarks
19

Clusters surrounding a charge Q in a plasma
An external charge Q polarizes the plasma medium
Medium charges of the same sign are pulled toward Q.
Medium charges of the opposite sign are pushed away from Q.
This is the familiar Debye screening with a screening radius r D
There is no net change of total medium density, to the first order
of (α/r D T) .
However, the second order term (α/r D T) 2 has the same sign for
charges of both signs. There is a net increase in total density
surrounding Q.
This increase in polarization charges can be large in a dense
medium.
20

A simple model of charge clustering
• Q
(charge +q) at -R/2
• Q (charge –q) at R/2
• medium: e + (charge +q), e - (charge –q)
• particles interact with an e 1 e 2 /r interaction
We assume e + and e - are massless and are
fermions.
We also assume local thermal equilibrium
21

1000
TS 1 [MeV]
(b)
500
0
R (fm)
r [fm
0 0.5 1 1.5
Lattice gauge calcualtions of TS 1 =U 1 -F 1 .
O. Kaczmarek et al. hep-lat/0506019
C.Y.Wong,Phys.Rev.C76,014902(’07)
24

(1)
Simple estimates of heavy quark parton cluster
(2)
25

Implications of a heavy quark parton cluster
• The motion of the heavy quark is that of a cluster of
particles and not just a single particle.
• The color charge of the heavy quark is substantially
screened by the cluster of medium charges.
• The clustering will enhance the (heavy-quark)-parton
cross section by the presence of associated particles.
• The degree of clustering will decrease in strength as the
p t of the heavy quark increases. Associated near-side
cluster yield decreases with increasing heavy quark pt.
• The cluster of particles show up experimentally as
associated particles in coincidence with the heavy quark.
These associated particles has characteristics different
from those associated with a light quark.
26

Conclusions
The momentum kick model
• describes near-side ridge data with light quark triggers
• provides information on early medium properties and jetmedium
interaction
• fails to describe near-side ridge data with heavy quark
(electron) trigger
Recent STAR near-side heavy quark jet data observations
• Number of associated with heavy quark is large
• CuCu yield is large relative to AuAu yield
There exists the clustering of medium particles surrounding
heavy quarks
We should explore whether parton clustering may be a possible
origin of the STAR observation of large number of particles
associated with heavy quarks
27

Additional details
28

Basic ideas of the momemtum kick model
• Ridge particles are medium partons kicked by
the jet and they acquire a momentum kick q
along the jet direction
• The kicked final partons subsequently
materialize as hadrons by parton-hadron duality
• The ridge particle distribution depends on the
initial parton momentum distribution and the
magnitude of the momentum kick q.
30

The width in Δφ depends on the magnitude of q.
at pt=2 GeV
32

To describe experimental data, we need
1. A good description of the “jet” component
2. A good description of the shape of the
normalized initial momentum distribution
3. We can then determine the jet-medium
interaction parameters by comparison with
data:
q, f R , f J
33

Centrality depedence of R AA & ridge yield
36

Distribution of the number of jet-(medium parton) collisions
37

The momentum kick model gives a good description of R AA
38

Centrality dependence in the momentum kick model
39

Energy and mass dependence in the momentum kick model
40

Possible evolution scenario of medium partons
41