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Collective motion of Xe-Xe collision at CSR energy

Xie Fei, Wu Kejun, Liu Fengccnu

Institute of Particle Physics

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Outline

Motivation Result and discussion• Centrality selection• Baryon density evolution • Collective flow• Thermalization and mT spectra

Summary

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1. Motivation

Matter Compression: Vacuum Heating:

High Baryon Density-- low energy collisions-- neutron starquark star

High Temperature Vacuum -- high energy collisions -- the Big Bang

Deconfinement

CSR energy

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1. Motivation

HIRFL-CSR

Building 2#

CSRm

CSRe

SFCSSC

SFC: up to 10 AMeV

SSC: up to 100 AMeV

North

Status and Prospects of HIRFL Experiments Hushan Xu

The Heavy Ion Research Facility in Lanzhou (HIRFL) Cooler Storage Ring (CSR)

CSRm: 500AMeV~1000AMeV

IonsCSRm 12C6+

36Ar18+

78Kr28+ 129Xe27+

CSRe 12C6+

36Ar18+

78Kr28+

ETF Phase IETF Phase I(External Target Facility – Phase I) Z.G. Xiao SQM2008(External Target Facility – Phase I) Z.G. Xiao SQM2008

detectors: 4 segmented Clover detectors

• ToF Wall: 3, 2 layers of BC408 bars, 30 bars/layer, readout from both ends with PMT (R7525)

• Neutron Wall: 14 layers, 18 paddles/layer, readout from both ends with PMT (R7724); BC408 only for the first two layers, sampling type (BC408+Fe) for the others

• MWDC: 6, with conventional technique

•For RIB Physics mainly

ETF Phase IIETF Phase IINew DetectorsNew Detectors

• -ball

(CsI(Tl) array•MWPC (inside dipole)• Si-strip array (inside dipole)• TPC? (at target region)

Possible PhysicsPossible Physics• For RIB Physics• For EoS of asymmetry nuclear matter• For high baryon density matter

Key part！！

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2.1 Centrality selection

Two methods:1. The multiplicity of forward neutrons with polar angle θ < 15◦ in the

laboratory frame.2. The multiplicity of charge particles Nch with mid-rapidity

linear dependence of the impact parameter b

. ./ 0.2C MY Y

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2.2 Baryon density

238 23892 92U U

129 12954 54Xe Xe

197 19779 79Au Au

R

5.7fm

6.3fm

Short (b -b) 5.8fm

Long (t -t) 9.4fm

max bE

maxdenT R

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2.3 Collective flow(1)

0

x

y

d pF

dy

v1 flow parameter:

xy z

3 2

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11 2 cos[ ( )]

2

cos[ ( )]

n rnt t

n r

d N d NE v nd p p dp dy

v n

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2.3 Collective flow(2)

0 0

( ) ( ) ( ) coulombU a b V

In ART model:

Mean field:

Soft : K=201MeV

Stiff : K=377MeV

Cascade : no mean field

are all functions of K , ,a b

Flow parameter is sensitive to

EOS.

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2.3 Collective flow(3)

CSR energy

At CSR energy region, around 500~1000MeV/u, it has very rich flow information, i.e. collision dynamics information.

Jean-Yves OllitraultaarXiv:nucl-ex/9802005 v1 12 Feb 1998

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F will get the maximum at about b/bmax=0.2 for different elements

bmax

Cu 9fm

Xe 12fm

Pb 14fm

2.3 Collective flow(4)

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2.4 Thermalization and mT spectra(1)

The Charge Multiplicity Nch

0~10%

10~30%40~60%

60~80%

Tslope (MeV) Error

0~10% 67.2 3.1e-4

10~30% 62.5 3.2e-4

40~60% 54.2 3.5e-4

60~80% 47.4 5.6e-4

2/Tm T

T T

d NAe

m dm dy

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2.4 Thermalization and mT spectra(2)

Tslope(MeV) Error

200MeV 45.1 1.9e-3

500MeV 51.5 8.6e-4

900MeV 68.9 8.0e-4

Tslope(MeV)

Error

200MeV 35.4 4.1e-4

500MeV 67.1 4.8e-4

900MeV 94.1 6.4e-4

(a) proton

(b) pion

2/Tm T

T T

d NAe

m dm dy

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Summary

We can use forward Neutron or Nch to determine the collision centrality

v1 flow is sensitive to the EOS and system size

Anisotropy flow reach its extremum at CSR energy range. The turnings contain rich dynamic information. This energy region is well worth studying for flow.

Radial collective motion is stronger at central collisions.