The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA Guo-Liang Ma/(SINAP)
AMPT simulations of isobaric collisions
Guo-Liang Ma
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⎯ 9640Zirconium vs 9644Ruthenium
This work is in collaboration with Xu-Guang Huang (FDU) and Wei-Tian Deng (HUST).
Shanghai Institute of Applied Physics, Chinese Academy of Sciences
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• Motivation
• The AMPT model (CME)
• Ru+Ru vs Zr+Zr
• Summary
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Outline
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
Chiral Magnetic Effect=> charge separation
•The RHIC data are consistent with the CME expectation (dipole charge separation).
PRL 103, 251601 (2009)
dipole
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Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
dipole charge separation
(1) Introduction
•We include initial dipole charge separation mechanism into AMPT model.We switch the py values of a percentage f% of the downward moving u quarks with those of the upward moving u-bar quarks, and likewise for d-bar and d quarks.
•We focus on final state effects on the charge separation, including parton cascade, hadronization, resonance decays.
•We do not include magnetic and electric fields, because we assume B and E vanish quickly.
G.-L. Ma, B. Zhang, PLB 700 (2011) 39
dipole
The AMPT model with CME charge separation
⇀ ⇀
u u u u
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f%=(N+upward-N+downward)/(N+upward+N+downward)
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
•The normal AMPT model underestimates the STAR data.•A constant initial charge separation ~10% can describe same-charge data in the presence of final state interactions.•From a percentage of charge separation of 10% in the beginning →1-2% percentage in the end.
G.-L. Ma, B. Zhang, PLB 700 (2011) 39
AMPT results on <cos(ϕa+ϕβ)>
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Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• We use Lienard-Wiechert potential to calculate the impact parameter b dependence of averaged <By> , perpendicular to the reaction plane.
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W.T. Deng and X.G. Huang, PRC 85, 044907 (2012)
b-dependent Magnetic field
<By>(0,0, t=0)
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
f%=(1146.1*A-4/3)*By(b)
• By fitting Au+Au and Cu+Cu data, we get the initial charge separation percentage f%=1146.1A-4/3By.
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b-dependent initial charge sep. percent
open: AMPT (10 mb)solid: Exp. data
blue: opp chargered: same charge
diamond: Au+Autriangle: Cu+Cu
f%=(N+upward-N+downward)/(N+upward+N+downward)~JπR2/Nmult~ A-4/3By
f%=1146.1A-4/3By(b)
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
⎯ 9640Zirconium vs 9644Ruthenium
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Zr+Zr and Ru+Ru 200 GeV
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
Glauber parameters for Zr96 and Ru 96
setting 2 R0 a(d) β2 β4
Ru96 5.0845 0.567 0.053 0.009
Zr96 5.0212 0.574 0.217 0.01
• Two opposite settings of Glauber parameters for Ru96 and Zr96 (http://nrv.jinr.ru/nrv/webnrv/map/).
• which is more ellipsoidal? Ru96 or Zr96?
setting 1 R0 a(d) β2 β4
Ru96 5.0845 0.567 0.1579 0.00
Zr96 5.0212 0.574 0.08 0.00
El.-Magn. properties
Radius[4,5,6] (fm) & Deformation[3]
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Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
Impact parameter dependence of elliptic flow
• v2 in Zr+Zr ≉v2 in Ru+Ru at small b due to ellipsoidal deformation. • v2 in Zr+Zr ≈v2 in Ru+Ru at large b, where B field differs largely. We
expect to see little v2 effect on CME signal difference.• We choose the setting 2 in the following CME study.
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Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA 11
• We calculate the b dependence of averaged <By> for Ru+Ru and Zr+Zr.
• <By>(Ru+Ru) is larger than <By>(Zr+Zr) by 10% at large b.
b-dependent Magnetic field
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• We apply f%=1146.1A-4/3By(b) to introduce the initial charge separation into Ru+Ru and Zr+Zr.
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b-dependent initial charge sep. percent
Centrality bmin (fm) bmax (fm)
0-10% 0 3.9
10-20% 3.9 5.5
20-30% 5.5 6.8
30-40% 6.8 7.8
40-50% 7.8 8.8
50-60% 8.8 9.6
60-70% 9.6 10.3
Centrality cuts for Ru+Ru and Zr+Zr
f%=1146.1A-4/3By(b)
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• We see a reasonable magnitude ordering that Au+Au < Ru+Ru, Zr+Zr < Cu+Cu.
diamond: Au+Au (STAR data)circle: Ru+Ru (AMPT CME)square: Zr+Zr (AMPT CME)triangle: Cu+Cu (STAR data)
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AMPT (CME) results on <cos(ϕa+ϕβ-2ѱ2)>
opp-charge
same-charge
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
initial state final state
• After final state interactions, the <cos(ϕa+ϕβ-2ѱ2)> difference between Ru+Ru and Zr+Zr tends to disappear.
circle: Ru+Rusquare: Zr+Zrblue:opp-chargered: same-charge
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<cos(ϕa+ϕβ-2ѱ2)> in Ru+Ru and Zr+Zr
(parton cascade, hadronization, resonance decays)
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• The CME effect increases the magnitude of <cos(ϕa+ϕβ-2ѱ2)> for both same- and opposite-charge correlations in Ru+Ru and Zr+Zr.
Ru+Ru Zr+Zr
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<cos(ϕa+ϕβ-2ѱ2)> with and without CME
open: AMPT (normal)solid: AMPT (CME)
opp-charge
same-chargeopen: AMPT (normal)solid: AMPT (CME) same-charge
opp-charge
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• If Ɣ=<cos(ϕa+ϕβ-2ѱ2)>, We define the CME contribution H by H=Ɣ(AMPT CME)-Ɣ(AMPT normal).
• Hopp and Hsame looks similar between Ru+Ru and Zr+Zr.
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different CME between Ru+Ru and Zr+Zr ?
3.8M eventsopp-charge
same-charge
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• The difference between two systems’ (Hopp-Hsame) could be seen in very peripheral collisions (50-70%). (It needs more event statistics.)
3.8M events
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different CME between Ru+Ru and Zr+Zr ?
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
initial state
final state
• After final state interactions (parton cascade, hadronization, resonance decays), the charge separation percentage decreases.
• But the ratio of f%(Ru+Ru) to f%(Zr+Zr) seems to keep, which is equal to <By>(Ru+Ru) /<By>(Zr+Zr).
red: Ru+Rublue: Zr+Zr
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Discussion I: final interaction effect on charge separation
f%(Ru+Ru)f%(Zr+Zr)
initial state final state
(parton cascade, hadronization, resonance decays)
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• If f%~A-4/3By2 , the relative f% ratio of Ru+Ru to Zr+Zr will be changed from <By>(Ru+Ru) /<By>(Zr+Zr) into <By>2(Ru+Ru) /<By>2(Zr+Zr). => The final CME signal difference between Ru+Ru and Zr+Zr can be enhanced.
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Discussion II: By dependence of initial charge sep. percentage
f%~A-4/3By
f%~A-4/3By2
initial state final state
f%=(N+up-N+down)/(N+up+N+down) ~ A-4/3By or A-4/3By2?
f%(Ru+Ru)f%(Zr+Zr)
Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
Summary
• Two major features found in AMPT simulations of isobaric collisions at 200GeV:
• v2 difference between central Ru+Ru and central Zr+Zr collisions⇒deformation shape of Ru and Zr.
• CME observable difference between peripheral Ru+Ru and peripheral Zr+Zr collisions (needs more statistics)⇒ CME difference due to different B fields.
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Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
Backup
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Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
open: AMPTsolid: Exp. data
Normal AMPT results on <cos(ϕa+ϕβ-2ѱ2)>
blue: opp chargered: same charge
diamond: Au+Autriangle: Cu+Cu
• The normal AMPT model underestimate the STAR data for Au+Au 200 GeV and Cu+Cu 200 GeV.
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Guo-Liang Ma/(SINAP)The QCD Workshop on Chirality, Vorticity and Magnetic Field in Heavy Ion Collisions, Feb.23-26, 2016, UCLA
• I check the case of Zr+Zr with same Glauber parameters as Ru+Ru.=> The effect of deformation on CME signal is small.
<cos
(ϕa+ϕβ
-2ѱ2
)>
centrality bin
open circle: RuRusolid square: ZrZropen square: ZrZr(same shape as RuRu)
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Shape effect on <cos(ϕa+ϕβ-2ѱ2)>
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