The physics mechanism of light and heavy
flavor vn and mass ordering in AMPT
Hanlin Li
Wuhan University of Science and Technology & Purdue University
Zi-Wei Lin
East Carolina University
Fuqiang Wang
Mostly based on:
Purdue University
L. He, T. Edmonds, Z.-W. Lin, F. Liu, D. Molnar, F.Q. Wang, Phys. Lett. B 735,506(2016)
Z.-W. Lin, T. Edmonds, L. He, F. Liu, D. Molnar, F.Q. Wang, QM'15, arXiv:1512.06465
H.L. Li, L. He, Z.-W. Lin, D. Molnar, F.Q. Wang, W. Xie, Phys. Rev. C 93,051901(R)(2016)
H.L. Li, L. He, Z.-W. Lin, D. Molnar, F.Q. Wang, W. Xie, arXiv:1604.07387v2
SQM，UC Berkeley 27 June- 1July 2016
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Outline
Introduction
Results and discussion
Vn development in AMPT
Origin of the mass splitting of Vn
Charm quark’s Vn
Summary
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Heavy ion collisions
Hard probes (pT,M>>ΛQCD=200 MeV)
Jet queching
Heavy quarks (tagged b-jets) .……
Soft probes (pT~ΛQCD=200 MeV)
Collective flow……
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Hydrodynamic vs transport
Hydrodynamics has been very successful
for global observables, especially flow vn
Heinz, BES Workshop at LBNL 2014
using viscous hydrodynamics.
Transport model can also
describe flow vn :
degree of equilibration is
controlled by cross section σ
Zhang, Gyulassy and Ko, PLB (1999)
using elastic parton transport.
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4
0
1
2 3 4
p (GeV/c)
5
06
1
2 3 4
pT(GeV/c)
5
60
A Multi-Phase Transport (AMPT) model describes data
T
FIG. 1: T he t ransverse moment um dependence of t he ellipt ic, v2 , and
Pb+ Pb collisions (lower panel) as obt ained in t he AMPT model (op
AMPT describes low-pt (<2GeV/c) πcent
& Krality
dataclasses
on are defined by t he number of produced charged pa
dN/dy, pT spectra & v2 in central & mid-central
small
s. colliding systems
ed by t he fullinpoint
T he CMS dat a are denotCollectivity
vn{2, |Dh|>2}
events of 200AGeV Au+Au & 2760AGeV Pb+Pb.
0.12
v2 (exp. data)
v3 (exp. data)
v2 (AMPT, 3 mb)
v3 (AMPT, 3 mb)
0.1
0.1
0.08
0.06
0.05
p+Pb 5.02 TeV
0.04
0.02
0
0
50 100 150 200 250 300
0
0
Ntrack
v2 of π & K (AuAu@200AGeV b=7.3fm)
Z.-W.Lin,PRC90 (2014) 1, 014904
FIG. 2: T he CMS dat a (full point s) vs t he AMPT model (open symb
Bzdak and Ma,
ellipt ic, v2 , and t riangular, v3 , flow coef f ci ient s in p+ Pb (left ) and
Phys.Rev.Lett. 113 (2014) 25, 252301
produced charged part icles, N t r ack , measured in |η| < 2.4 and pT > 0
5
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27
June1July
2016
and antiquarks which undergo elastic scat terings (in con-
mo
Parton v2
Parton azimuthal anisotropy developed in AMPT
• Partons freeze out with large
positive v2, even when they
do not interact at all.
• This is due to larger escape
probability along x than y.
• Remaining partons start off
with negative v2, and become
~isotropic (v2~0) after one
more collision.
• Process repeats itself.
• Similar for v3.
• Similar for d+Au collisions.
L. He, T. Edmonds, Z.-W. Lin,
F. Liu, D. Molnar, F.Q. Wang,
Phys. Lett. B 735,506(2016)
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Majority anisotropy from escape
v2 from Random Test:
purely from escape mechanism, not from collective flow
ϕ randomized
AMPT results on integrated v2:
Normal ϕ randomized
Au+Au
3.9%
2.7%
d+Au
2.7%
2.5%
% from escape
69%
93%
L. He, T. Edmonds, Z.-W. Lin,
F. Liu, D. Molnar, F.Q. Wang,
Phys. Lett. B 735,506(2016)
Majority of anisotropy comes from the “escape mechanism”
The contribution to anisotropy from hydrodynamic-type collective flow is found to be small.
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The mass splitting of vn
What’s origin of the
mass splitting?
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Partonic vn
H.L. Li, et al, arXiv:1604.07387v2
H.L. Li et al, Phys. Rev. C 93,051901(R)(2016)
The mass splitting of partonic anisotropy may be caused by mass difference
rather than collective flow.
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0.15
0.15
v2
hadronvor
parton v
2 after decay
2
Mass splitting from coalescense and hadronic rescattering
200 GeV
Au+Au
Au+Au,
200
GeV
|h|<1
(a)
Normal
p±
K±
p(p)
0.05
0.05
0.05
c.q.v
2
p± after coal.
00
00
0.50.5
1
1
200
GeV
(b)
Rndm
f d+Au
|h|<1
1.5
K ± after coal.
p(p) after coal.
1.5
0
2
2
00
0.5
0.5
1
1
1.5
1.5
0.5
(b) d+Au
200 GeV
before rescatt.
p±
p(p)
1
1.5
after rescatt.
p±
p(p)
2
0.05
p±
K±
p(p)
0.05
0
0.1
0.1
0.05
0
0
(a) Au+Au
200 GeV
0.1
0.1
0.1
0.1
0.15
0.15
2
2
hadron p (GeV/c)
p (GeV)
0
0
0.5
1
1.5
2
p (GeV/c)
H.L. Li et al, Phys. Rev. C 93,051901(R)(2016)
The mass splitting is reduced by decays but significantly increased by hadronic scatterings.
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v2
Origins of vn mass splitting
0.1 (a) Au+Au
H.L. Li, et al, arXiv:1604.07387v2
0.05
p = (0.7-0.8) GeV/c
1
(b) d+Au
2
p±
p(p)
±
K
3
h±
t(fm/c)
0.06
0.04
prim.
w/ decay w/ rescatt.
w/ decay
H.L. Li et al, Phys. Rev. C 93,051901(R)(2016)
The mass splitting is due to coalescence and, more importantly, hadronic
rescatterings.
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Charm quark
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Charm quark
Look at light and charm quark freeze out v2 at the same proper
time (same geometry).
v2 vs. proper time is same for light and charm quark, suggesting
common escape mechanism.
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Summary
I.
The anisotropic parton escape is the dominant source of
azimuthal anisotropy of light quark in transport model.
II. The mass splitting of vn is due to coalescence, and more
importantly, hadronic rescatterings.
III. Charm and light quark v2 mechanisms appear to be the same in
pPb.
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Back up
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Azimuthal anisotropies
coordinate space
•
Coordinate space configuration anisotropic (almond
shape) however, initial momentum distribution
isotropic (spherically symmetric)
•
Only interactions among constituents generate a
pressure gradient, which transforms the initial
coordinate space anisotropy into a momentum space
anisotropy (no analogy in pp)
•
Multiple interactions lead to thermalization -> limiting
behavior ideal hydrodynamic flow
y
x
Momentum space
d 3N 1 d 2 N æ ¥
çç1+ å 2vn cos n f - Yr
E 3 =
d p 2p pt dpt dy è n=1
((
((
))
vn = cos n f - Yr ,
f = tan (
-1
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py
px
))
ö
÷÷
ø
)
16
Decays
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Hadronic rescatterings
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Hadronic eccentricity