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Isospin effects in neutron and proton flows

Isospin effects in neutron and proton flows. by Qingfeng Li @ FIAS , (AvH fellow, Host: Horst Stöcker). Thanks: Marcus Bleicher, Sven Soff, Zhuxia Li. Outline. Our purpose -and- many observables The isospin effect on nucleons The flows and the differential flows

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Isospin effects in neutron and proton flows

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  1. Isospin effects in neutron and proton flows by Qingfeng Li @ FIAS, (AvH fellow, Host: Horst Stöcker) Thanks: Marcus Bleicher, Sven Soff, Zhuxia Li

  2. Outline • Our purpose -and- many observables • The isospin effect on nucleons • The flows and the differential flows • The importance of precise measurement on neutrons • Good future, laborious work. Qingfeng Li for GSI 2006

  3. The purpose The uncertainty in symmetry term, especially in the density dependence of symmetry energy Obviously, it is closely related to Astrophysics and neutron-rich structure and reaction physics (with large neutron access). Qingfeng Li for GSI 2006

  4. Normal Observables • Particle species: emitted neutrons and protons, resonances (), Sigmas, light and heavy fragments, mesons (pions, kaons,etc) • Single-particle observables: excitation function of particle multiplicities, (transverse)momentum-/energy-/rapidity- distribution, momentum quadrupole (Qzz), radial-/direct-/elliptic- flows,… • Two-particle correlations: HBT (coordinate-momentum corr.), angular correlation, … Qingfeng Li for GSI 2006

  5. “New” observables • Single-/double- negatively/positively charged particle (nucleons, pions, kaons, etc) ratios from Ru/Zr+Zr/Ru (mass symmetric but isospin asymmetric) reactions (FOPI), or from Sn-isotope reactions (Michigan). • Vartl, (FOPI), or Rt/l=dN/dYx/dN/dYz • flow difference/differential flow (Fn-p,v2pm) of negatively-positively charged particles Qingfeng Li for GSI 2006

  6. To study the isospin effects • Nucleons are still one of the most sensitive candidates, which should be preferentially considered • Now, experimentally, it is able to measure neutrons with much more higher precision. Hmmm, right?  • Other particles? Of course important, but raise more uncertainties. As the first step, I suggest to measure neutrons and protons. Qingfeng Li for GSI 2006

  7. + + Many efforts • At quite low densities (/0=0.01-0.05) Nucl-ex/0602023 • At subnormal densities (compared with BUU): • At supranormal densities:  ~ 0.3 ? Qingfeng Li for GSI 2006

  8.   Symmetry energy effects on nucleons S-I S-II 2005-PhysRevC_72_034613 Qingfeng Li for GSI 2006

  9. Flows and differential transverse flow • To explore the medium at early stage when the central density is high. • The differential transverse flow suggested by Bao-An: • The multiplicities of nucleons should be firstly nicely reproduced by model. If Qingfeng Li for GSI 2006

  10.  Pion elliptic flow difference At pt~0.2-0.5 GeV/c, v_2^pm reflects explicitly the density dependence of sym.ene. at u>1. IE @ supranormal densities! Eb=800A GeV b=7-9 fm ZPA352,171(1995): by Bass, Hartnack, etal (neutron squeeze-out) PLB 562, 215(2003): by Greco, Baran, etal (neutron-proton v2 difference) 2006-JPG_32_151 Qingfeng Li for GSI 2006

  11. Nucleon double ratio from Ru/Zr+Zr/Ru Advantage: to show simultaneously the dependence on symmetry energy and the degree of isospin equilibrium The symmetry energy effect On FD is enhanced when Eb~400A MeV, b/b0~0.5 Others: Bao-An Li et al.: (using Sn isotoptes) Double N/P ratio: Phys.Lett.B634:378-382,2006 Double pi-/pi+ ratios: Phys.Rev.C73:034603,2006 Double N-P differential flow : nucl-th/0606003   2006-PhysRevC_73_051601(R) Qingfeng Li for GSI 2006

  12. Isopin dependent medium effects on N-N elastic cross sections MF and C come from the same Lagrangian. They are both isospin dependent 2006-JPG_32_407 Qingfeng Li for GSI 2006

  13. At Eb~400A MeV • When comparing with those at Eb< 100A MeV: more IMF, excitataion energies of IMF are also large. They will decay (statistically/promptly/sequentially?) afterwards. The isospin-asymmetric and high-excited IMF play important role in final results. • The treatment of isospin effects on the late stage (in some after-burner program) should be paid more attention. (When to terminate the transport computation?) Qingfeng Li for GSI 2006

  14. My suggestions • Experimentally: • Multi-systems and Multi-observables. such as: Zr+Ru/Ru+Zr and Sn132+Sn124/Sn112+Sn112 For nucleons: multiplicities, (hence, the transverse momdnetum of n/p ratio), transverse and elliptic flows (hence, the flow diff./diff.flow) are required to measure. • Higher precision. (at least, errors should be well <10%) • Theoretically: • A completely self-consistent and relativisitic transport model (at least, in the N-- system)+ a good after-burner program are indispensable, since the isospin effects are small. Qingfeng Li for GSI 2006

  15. Outlook • Not easy, (effect is small, many uncertainties in theory/models) • but of great value. (neutrons, neutron flows, flow differentials) • Optimistic Thanks Qingfeng Li for GSI 2006

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