1 Heavy Ion Collisions at LHC in a Multiphase Transport Model A multi-phase transport (AMPT) model ...
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Heavy Ion Collisions at LHC in a Multiphase Transport Model
A multi-phase transport (AMPT) model Rapidity and transverse momentum distributions Anisotropic flows: elliptic & hexadecupole Two-pion and two–kaon interferometries Thermal charm production Jet flavor conversions
L.W. Chen1, B.A. Li2, Z.W. Lin3, B.W. Zhang4,B. Zhang5, C.M Ko6
1Shanghai Jiao Tong Univ., 2Texas A&M Univ.-Commerce3East Carolina Univ., 4Huazhong Normal Univ. 5Askasas State University, 6Texas A&M University
Work supported by NSF and Welch Foundation
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A multiphase transport (AMPT) model
Default: Lin, Pal, Zhang, Li & Ko, PRC 61, 067901 (00); 64, 041901 (01);
72, 064901 (05); http://www-cunuke.phys.columbia.edu/OSCAR
Initial conditions: HIJING (soft strings and hard minijets) Parton evolution: ZPC Hadronization: Lund string model for default AMPT Hadronic scattering: ART
Convert hadrons from string fragmentation into quarks and antiquarks Evolve quarks and antiquarks in ZPC When partons stop interacting, combine nearest quark and antiquark to meson, and nearest three quarks to baryon (coordinate-space coalescence) Hadron flavors are determined by quarks’ invariant mass
String melting: PRC 65, 034904 (02); PRL 89, 152301 (02)
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Pb+Pb @ 5.5 TeV
Particle multiplicity at LHC increases by a factor of ~ 4 from that at RHIC
Rapidity distributions
σparton=10 mb
b< 3 mb
b< 3 mb
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Transverse momentum distributions
Particle transverse momentum spectra are stiffer at LHC than at RHIC → larger transverse flow
0 < b < 3 fm
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Quark elliptic flows
Quark elliptic flows are larger at LHC than at RHIC, reaching ~ 20%
Au+Au @ 200 GeV
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Pion and Proton Elliptic flow at LHC
Elliptic flow is larger for pions but smaller for protons at LHC than at RHIC
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Heavy meson elliptic flows at LHC
)p)m/m((v)p)m/m((v)p(v TMqq2,TMqq2,T2M 2211
Quark coalescence model
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Light Quark and pion hexadecupole flows at LHC
naïve coalescence model
65.0v
v
2
1
4
1
v
v2q2,
q4,
2M2,
M4, 8.0v
v2M2,
M4,
AMPT model
~1.2 at RHIC
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Strange Quark and phi hexadecupole flows at LHC
65.0v
v
2
1
4
1
v
v2s2,
s4,22,
4,
Coalescence model AMPT model
95.0v
v22,
4,
~1.2 at RHIC
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Deuteron elliptic flow at LHC
Filled circles: proton v2 from AMPT Dotted line: fitted proton v2
Dashed line: deuteron v2 from coalescence model including deuteron wave function effect Solid lines: deuteron v2 from a dynamic model based on reactions NN→dπ and NNN→dN
Coalescence model is a very goodapproximation for weakly bound particles
Pb+Pb @ 5.5 TeV, b=8 fm
Y. Oh & CMK
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Radii from Gaussian fit to correlation functions
3
1i
2i
2ii2 K)Q(Rexp1)K,Q(C
Source radii for pions are larger than for kaons and both are larger at LHC than at RHIC
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Emission source functions
Shift in out direction
- Strong correlation
between out position
and emission time
- Large halo due to
resonance (ω) decay
and explosion
→ non-Gaussian source
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Thermal charm production in QGP B.W. Zhang & CMK
• Large thermal charm production• Next-leading order and leading order contributions are comparable• Insensitive to gluon masses• Effect reduced by about 2 for initial temperature T0=600 MeV or for mc=1.5 GeV
mc=1.3 GeV
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Jet conversions in QGP
Elastic process: qg→gq
Inelastic process: ggqq
Quark jet conversion
Gluon jet conversion: similar to above via inverse reactions
Gluon is taken to have a larger momentum in the final state
W. Liu, B.W. Zhang & CMK
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Proton to π+ ratio at high transverse momenta
p/π ratio similar to that in p+p collisions at RHIC when quark and gluon conversion widths are multiplied by KC~4-6. It is lower than p+p at LHC.
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Summary
Compared to RHIC, heavy ion collisions at LHC have:
~ factor of 4 larger charged particle multiplicity larger transverse flow larger elliptic flow for pion and smaller one for protons large heavy quark and meson elliptic flows smaller v4/v2
2 ratios for both quarks and hadons
smaller two-pion and two-kaon correlation functions
and larger source radii enhanced thermal charm production smaller p/pi ratio at high pT than in p+p