Transcript Two-charged-particle azimuthal angle correlation as another

Anisotropic flow, Azimuthal Balance Function,
and Two-charged-particle Azimuthal Correlations
in RQMD and AMPT
IOPP, Central China Normal University, Wuhan, China
1. Introduction
2. Behaviors of these three measurements
in RQMD and AMPT
3. Conclusions and Suggestions
We are very grateful to Zhixu Liu and Jiaxin Du for offering us the data
samples of RQMD and AMPT.
1. Introduction
► Anisotropic collective flow is caused by initial
spatially-anisotropic participant zone and interactions
in non-central nucleus-nucleus collisions,
v2 ( pt ) 
v2 ( )  cos 2(  R )
p x2  p y2
p x2  p y2
ψR is azimuthal angle of reaction plane
defined on an event-by-event base.
The observed large flow at RHIC has been argued as an
indicator of early thermal equilibrium. Its flavor dependence is
supposed to be highly relevant to interpretation of strongly
interacting QGP.
J. Adams, et al, (STAR Coll.), Nucl. Phys. A 757, 102(2005);
K. Adcox, et al, (PHENIX Coll.), Nucl. Phys. A 757, 184(2005).
Miklos Gyulassy, Larry McLerran, Nucl. Phys. A 750, 30-63(2005).
B. M\"uller, Annu. Rev. Nucl. and Part. Phys.,1(2006).
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1. Introduction (cont.)
►Azimuthal charge balance function
1  n  ( )  n  ( ) n  ( )  n  ( ) 
B ( )  


2
n
n

__ T f = 90 MeV, β=0.6
- - T f = 165 MeV β=0.5
☺Another independent constraint
on the temperature and the
amount of transverse flow at the
freeze-out.
☺It is expected from the thermal
model that the higher temperature
and the smaller elliptic flow, the
wider the azimuthal balance
function.
P. Bozek, Phys. Lett. B 609, 247(2005).
It is interesting to see how azimuthal charge balance function
behaves in the dynamical models RQMD and AMPT.
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1. Introduction (cont.)
► Two-charge-particle azimuthal corr.
C ab ( ) 
nab ( )
nab
L. Foa, Phys. Reports 22(1975).
nab(δφ): is the number of pairs of charged a and b particles satisfying the
criteria that their relative angle equals δφ.
nab: is the total number of the same kind of pairs for all possible separated angles.
K. Adcox, et al., (PHENIX Coll.), PRL 89, 212301(2002)
► Why we choose these three measurements ?
☻ They are all anisotropic trans. momentum dis. related.
☻ The behaviors of these three measurements in RQMD and AMPT will help
us in understanding the underlying dynamics.
☻ Both two-charge-particle azimuthal corr. and azimuthal charge balance
func. are reaction plane irrelevant and therefore easily to measure.
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1. Introduction (cont.)
► Models
RQMD (v2.4):
Au-Au collisions at √s NN=200GeV
A MC generator of Relativistic Quantum Molecular Dynamics ( hadron ),
Without hadron rescattering, v2 = 0;
With hadron rescattering, v2 > 0, but smaller than the data.
H. Sorge, Phys. Rev. C52, 3291 (1995).
See Feng Liu’s talk in the same session.
AMPT:
A MC generator of A Multi-Phase Transport Model (parton + hadron)
Default AMPT, v2 > 0, but still smaller than data;
AMPT with string melting, where parton transportation,
hadron rescattering and quark coalescence at hadronization are
implemented in the model. This model reproduces v2 (pt) data
at RHIC.
Zi-Wei Lin, Che Ming Ko, Bao-An Li, Bin Zhang
and Subrata Pal, Phys. Rev. {\bf C72}, 064901 (2005).
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2. Behaviors of three measurements in models
► v2 of all, positive and negative charged particles
RQMD without rescattering:
no v2 at all.
RQMD with rescattering:
same middle values
of vc2 , v-2, v+2.
AMPT with string melting:
same big values of
vc2 , v-2, v+2
v2 is the biggest for mid-central
coll. and is smaller for central
and very peripheral collisions.
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2. Behaviors of three measurements in models
► Ccc, C
++
, C– and C+- in RQMD
Rescattering off:
☺ No small angular corr.
☺ Large angular corr. due to
momentum conservation.
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Rescattering on:
☺ Small angular corr. appear!
☺ The diff. among them are
small but visible.
☺ Large angular corr. remains.
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2. Behaviors of three measurements in models
► Centrality dependence of Ccc, C
++
, C-- , C+-, in RQMD
Rescattering off: Momentum conservation leads to the observed large
angular correlations, especially for the most peripheral collisions.
Rescattering on: The small angular corr. are the strongest for the
mid-central coll. , small for most central coll. and even smaller for the
most peripheral coll. This centrality dependence is the same as v2 .
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2. Behaviors of three measurements in models
► Ccc, C
++
, C-- , C+- in AMPT with string melting
In AMPT, small angular corr. becomes stronger than large angular corr.
Difference among Ccc, C ++ , C-- , and C+- are very small.
► Centrality dependence of Ccc, C ++ , C-- , C+- in AMPT
Small angle corr. have the same centrality dependence as flow.
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2. Behaviors of three measurements in models
► Two-charge-particle corr. from PHENIX Coll.
Data show:
●A anisotropic corr.
pattern is symmetric
about ∆ 900;
●This anisotropy
increase with impact
parameter and pt.
K. Adcox, et al, Phys. Rev. Lett. 89, 212301(2002)
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Models show:
► The small angle corr.
is related to anisotropy
of pt distribution
► The same symmetry
structure in AMPT
with string melting.
► The same centrality
dependency in both
RQMD and AMPT
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2. Behaviors of three measurements in models
► Azimuthal charge balance function in RQMD
RQMD w/o
RQMD w
No centrality dependence.
This means that the corr.
caused by momentum cons.
are cancelled in the measurement.
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The more central coll., the narrower BF,
which are diff. from centrality
dependence of v2 .
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2. Behaviors of three measurements in models
► Azimuthal charge balance function in
AMPT
__ T f = 90 MeV, β=0.6
- - T f = 165 MeV β=0.5
In more central coll., the BF is narrower
In more periph. coll., the BF is wider.
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This is different from the
expectations from the
thermal model, where the
smaller elliptic flow, the
wider azimuthal balance
function.
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3. Conclusions and suggestions
The behaviors of anisotropic flow, azimuthal charge
balance function, and two-charge-particle azimuthal corr.
in RQMD and AMPT are compared.
● The large angular corr. are due to the constraint of
momentum conservation.
● The small angular corr. mainly come from anisotropic
transverse momentum distribution caused by hadron
level rescattering and/or parton level transportation.
● The centrality dependence of the small angular corr.
is the same as the centrality dependence of v2
in both AMPT and RQMD.
● To measure the two-charge-particle azimuthal corr.
at STAR detector, where TPC covers the whole
azimuthal angle.
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3. Conclusions and suggestions
● From the behavior of two-charge-particle azimuthal
corr., we see that azimuthal charge balance function
(ACBF) well cancel the contributions caused by the
constraint of momentum conservation.
● ACBF changes monotonically with centrality in both
RQMD and AMPT models. This is different from the
centrality dependence of v2 and what expected from
thermal model.
● It is interesting to see how the B( ∆φ) behave in
current heavy ion collisions.
● These three measurements are all sensitive to the
anisotropic transverse momentum distributions.
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Appendix
AMPT default
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