1 Collective motion of Xe-Xe collision at CSR energy Xie Fei, Wu Kejun, Liu Feng ccnu Institute of Particle Physics

2 Outline  Motivation  Result and discussion Centrality selection Baryon density evolution Collective flow Thermalization and m T spectra  Summary

3 1. Motivation Matter Compression:Vacuum Heating: High Baryon Density -- low energy collisions -- neutron star  quark star High Temperature Vacuum -- high energy collisions -- the Big Bang Deconfinement CSR energy

4 1. Motivation HIRFL-CSR Building 2# CSRm CSRe SFC SSC 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 Ions CSRm 12 C Ar Kr Xe 27+ CSRe 12 C Ar Kr 28+

ETF Phase I (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 II New Detectors  -ball (CsI(Tl) array MWPC (inside dipole) Si-strip array (inside dipole) TPC? (at target region) Possible Physics For RIB Physics For EoS of asymmetry nuclear matter For high baryon density matter Key part ！！

7 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 N ch with mid-rapidity linear dependence of the impact parameter b

8 2.2 Baryon density R 5.7fm 6.3fm Short (b -b) 5.8fm Long (t -t) 9.4fm

9 2.3 Collective flow(1) v 1 flow parameter : x y z

Collective flow(2) In ART model: Mean field: Soft : K=201MeV Stiff : K=377MeV Cascade : no mean field are all functions of K Flow parameter is sensitive to EOS.

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 Ollitraulta arXiv:nucl-ex/ v1 12 Feb 1998

12 F will get the maximum at about b/b max =0.2 for different elements b max Cu 9fm Xe 12fm Pb 14fm 2.3 Collective flow(4)

Thermalization and m T spectra(1) The Charge Multiplicity Nch 0~10% 10~30% 40~60% 60~80% T slope (MeV)Error 0~10% e-4 10~30% e-4 40~60% e-4 60~80% e-4

Thermalization and m T spectra(2) T slope (MeV)Error 200MeV e-3 500MeV e-4 900MeV e-4 T slope (MeV)Error 200MeV e-4 500MeV e-4 900MeV e-4 (a) proton (b) pion

15 Summary  We can use forward Neutron or Nch to determine the collision centrality  v 1 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.