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Determining the Special Orientations in Deformed 238 U + 238 U Collisions at CSR

Determining the Special Orientations in Deformed 238 U + 238 U Collisions at CSR. Kejun Wu 1 , Fei Xie 1 , Feng Liu 1 , Nu Xu 1,2 1) Institute of Particle Physics, Huazhong Normal University, China 2) Nuclear Science Division, LBNL, Berkeley, CA 94720, USA. Outline. Motivation

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Determining the Special Orientations in Deformed 238 U + 238 U Collisions at CSR

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  1. Determining the Special Orientations in Deformed 238U+238UCollisions at CSR Kejun Wu1, Fei Xie1, Feng Liu1, Nu Xu1,2 1) Institute of Particle Physics, Huazhong Normal University, China 2) Nuclear Science Division, LBNL, Berkeley, CA 94720, USA Outline • Motivation • Results and discussions • Summary and Outlook --- Orientation Effect on High Density Matter --- Selecting those Events with High Density IWND2009, Shanghai, China, August 23~25

  2. Motivation : Why UU? Two most special geometry orientations Advantages and Suggestions: PRC 61,021903 (2002) PRC 61,034905 (2003) PRL 94,132301 (2005) PRC 72, 037901 (2005) PRC 73,034911 (2006) PRC 76, 051902(R) (2007) … tip-tip ( Two extreme collision condition ) ★Besides large atomic weight, Uranium is the most deformed stable nucleus. ★Longer duration for central tip-tip --- Higher local baryon density and easier thermalization ★Large initial eccentricity for central body-body ---Strong anisotropy flow IWND2009, Shanghai, China, August 23~25

  3. Motivation: QCD phase diagram ★ Emax =520MeV for U in CSR. ★ For tip-tip UU,medium has high temperature and density, partonic phase may be achieved. ★ CSR could make significant contribution in searching for the possible phase boundary. ★ Find a proper probe to study EoS and Chiral symmetry restoration. Cross-over CSR The Heavy Ion Research Facility in Lanzhou (HIRFL) - Cooler Storage Ring (CSR) IWND2009, Shanghai, China, August 23~25

  4. ART (a Relativistic Transport) Model The ART model was developed from the Boltzmann-Uehling-Uhlenbeck (BUU) model. BUU equation describes the time evolution of single particle in phase space. G.F.Bertsch and S.Das Gupta,Phys.Rep.160,189(1988). More baryon/meson resonances and their interactions are included. The maximum beam energy is 15 GeV/nucleon. • The particle-in-cell method of hydrodynamics • Divide the phase space into cells and set suitable test particles. • Evolving the test particle by Newton mechanics. • The initial condition the particle are distributed uniformly with a radius parameter of r0=1.12 fm. the momentum distribution is given by local Fermi gas approximation. • The collision integral is treated by dividing the ensemble of test particles into individual INC( intra-nuclear cascade) simulations. 1) B.A.Li and W.Bauer,Phys.Lett.B 254,335(1991);Phys.Rev.C 44,450(1991)。 2) B.A.Li and W.Bauer,and G.F.Bertsch,Phys.Rev.C 44,2095(1991)。 IWND2009, Shanghai, China, August 23~25

  5. Central Local Density UU vs. AuAu ( Full stopping for pp) b=0 fm ART 1.0, Energy and baryonic number conservation Tlab=500MeV Zhuang P.F, Nuclear Physics Review, Vol.19,No.3 Sep.,2002 • The maximal local baryon density can large than 3.2ρ0. • Longer duration in tip-tip UU than AuAu, even 2 times of body-body. • Baryon and energy density profile are similar. IWND2009, Shanghai, China, August 23~25

  6. Initial Geometry of Random Orientation θT,P：X-Z plane -π/2 ~π/2 φT,P ：X-Y plane 0~2π tip-tip: θT =θP=0 ,φT φp random body-body: θT=θP= ±π/2, φT=φp±π • Non-polarized U random orientation • Ideal tip-tip and body-body events are quite unusual. • Our goal is to select central tip-tip like events. What are the tip-tip like events? How to get the tip-tip like events ? IWND2009, Shanghai, China, August 23~25

  7. Centrality Dependence on Baryon Density bmax=13fm for tip-tip bmax=19fm for body-body Define: is central cube with 1fm3 The most interesting events are tip-tip collision with b<2.6 fm , which might be selected by measuring distinctively the forward neutron multiplicity. S>70 IWND2009, Shanghai, China, August 23~25

  8. OrientationDependence on Baryon Density θ effect in central collisions Φ effect in central collisions • S is independent on φ when θ is fixed. ( Only for central events ) • θ <200 if s>70 IWND2009, Shanghai, China, August 23~25

  9. Open Questions • What are the central tip-tip like events? As a rough estimate, those events should be with b<2.6fm (central) and θT，P <20°(tip-tip like). • How to determine those events in the experiment? Firstly, find certain measurable (Nn or Nch)as online analysis to scale centrality and gain the sub-sample with small b . Secondly, find some special observables as offline analysis to select those events withsmall θT，P. IWND2009, Shanghai, China, August 23~25

  10. Determining the Central Events b<=2.6fm 4fm<b<=6fm 2.6fm<b<=4fm • Nn cut for online analysis is satisfying. • In order to further enhance those events, offline analysis is needed. IWND2009, Shanghai, China, August 23~25

  11. Nuclear Stopping Power In low energy region, H.Kruse et al.,PRC 31,1770(1985) When the ratio R is about 1, indicating that the hadronic system might reached thermal equilibrium. • R cut for offline analysis is satisfying. IWND2009, Shanghai, China, August 23~25

  12. The purity of tip-tip like Events Total 402K, b<2.6fm 20K,tip-tip like (all particles) TOF acceptance (charge particles with θ<80°) No PID (charge particles with θ<80°and regarded as nucleons) • The purity can be improved when R and Nn cut are used together. IWND2009, Shanghai, China, August 23~25

  13. Summary and Outlook • The events with extended high density phase (the central tip-tip like events) are with b<2.6fm and θT,P<20°. • Using the forward neutron multiplicity (e.g. Nn<=40) as online analysis in CSR experiment is recommended. This can hold the central events effectively. As an additional result, the body-body like events can be rejected effectively by cutting Nn. • Using nuclear stopping power (e.g. R/Rc/Rc*) as offline analysis can select effectively the central tip-tip like events. • We expect the available UU data can be analyzed. Thanks！ IWND2009, Shanghai, China, August 23~25

  14. Basic models for heavy-ion collisions IWND2009, Shanghai, China, August 23~25

  15. X Long axis Z Y X Φ1 Long axis θ1 θ X θ2 Z Φ2 Rotation of colliding nuclei: Y Beam direction: Z T=RZ(Φ)*RY(θ) Rotation Matrics: Y IWND2009, Shanghai, China, August 23~25

  16. Y (2) (1) (4) θ1 Z θ1 (3) Y (2) Y (4) Φ angle (1) θ1 Z X θ1 (3) (1) tip-tip like collision Beam direction: Z (2)body-body like collision IWND2009, Shanghai, China, August 23~25

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