An incomple and possibly biased overview theoretical studies

An incomple and possibly biased overview: theoretical studies on symmetry energy Bao-An Li & collaborators: Jeff Campbell, Michael Gearheart, Joshua Hooker, Ang Li, Weikang Lin, Li Ou, Will Newton and Yuan Tian, Texas A&M University-Commerce Lie-Wen Chen, Shanghai Jiao Tong University Chang Xu, Nanjing University, Nanjing, China Che-Ming Ko and Jun Xu, Texas A&M University, College Station Zhigang Xiao and Ming Zhang, Tsinghua University, China Gao-Chan Yong, Institute of Modern Physics, China • Why is the density-dependence of nuclear symmetry energy still very uncertain? • What can we say with some confidence about the symmetry energy near the saturation density? • What are the major issues at low densities? • What are the new issues besides the unresolved old ones at suprasaturation densities?

The multifaceted influence of the isospin dependence of strong interaction and symmetry energy in nuclear physics and astrophysics A. W. Steiner, M. Prakash, J. M. Lattimer and P. J. Ellis, Phys. Rep. 411, 325 (2005). (Effective Field Theory) n/p π-/π+ t/3 He K+/K 0 (QCD) Isospin physics in Terrestrial Labs isodiffusion isotransport isocorrelation isofractionation isoscaling

Esym (ρ) predicted by microscopic many-body theories d Symmetry energy (Me. V) F r. H e n ry o e h dt l e i e f l. ) v i t ec r et a f f E ise (Ka Di ra B c- ck e u r R t ela iv ic ist n ea el i F M Brueckner HF Greens function Variational many-body Density A. E. L. Dieperink et al. , Phys. Rev. C 68 (2003) 064307

The Esym (ρ) from model predictions using popular effective interactions Examples: ρ 23 RMF models Density L. W. Chen, C. M. Ko and B. A. Li, Phys. Rev. C 72, 064309 (2005); C 76, 054316 (2007).

Relation between symmetry energy and the mean-field potential Lane potential kinetic Symmetry energy Effective mass J. Dabrowski, Physics Letters 8, 90 (1964) isoscalar isovector

Why is the symmetry potential/energy so uncertain? • Short-range tensor force due to rho meson exchange • Isospin-dependence of NN correlations and the tensor force • Spin-isospin dependence of 3 -body forces Within an interacting Fermi gas model: Structure of the nucleus, M. A. Preston and R. K. Bhaduri (1975) NN correlation functions Isospin-dependence of strong interaction: Nucleons having isospin t=1/2 t 3=1/2 for neutrons t 3=-1/2 for protons T=0 or 1 for NN pairs

S 12=2 S=1, T=0

Uncertainty of tensor force at short distance Takaharu Otsuka et al. , PRL 95, 232502 (2005); PRL 97, 162501 (2006) Cut-off=0. 7 fm for nuclear structure studies or s n te y+ n g Go Gogny

Tensor force contribution to symmetry energy G. E. Brown and R. Machleidt, Phys. Rev. C 50, 1731 (1994). S. -O. Bacnman, G. E. Brown and J. A. Niskanen, Phys. Rep. 124, 1 (1985). PLB 18, 54 (1965)

Effects of short-range tensor force on symmetry energy Ang Li and Bao-An Li, 2011

Density dependence of the symmetry energy is the main criterion for distinction between Skyrme parameterizations (87 tested) Group I 27 Group III 33 27 J. R. Stone et al. , PRC 68, 034324 (2003) Original Skyrme potentials have tensor components, but they are normally dropped in SKF calcluations Page 3

D. Vautherin and D. M. Brink, Phys. Rev. C 5, 626 (1972) + MANY other papers starting from the same 3 -body force, Necessary to fit the saturation properties of nuclear matter Reduced to different 2 -body force with α=1/3, 2/3, 1, etc α controls the in-medium many-body effects x 0 controls the mixing of different spin-isospin channels

Effects of the 3 -body force on the symmetry energy X 0 from -1. 56 to 1. 92 are used in the over 140 effective interactions in the literature Chang Xu and Bao-An Li, PRC 81, 044603 (2010).

Isospin-dependence of Short Range NN Correlations and Tensor Force Two-nucleon knockout by an electron R Subedi et al. Science 320, 1475 (2008) M. Strikman, CERN Courier Jan 27, 2009 H. Baghdasaryan et al. (CLAS ollaboration) Phys. Rev. Lett. 105, 222501 (2010) np pp

Isospin dependence of nucleon-nucleon correlation due to tensor force and its effects on single-particle momentum distribution Tensor force + Repulsive core Ann. Rev. Nucl. Part. Sci. , 21, 93 -244 (1971) Fermi sphere Repulsive core only

Effects of isospin-dependence of short-range nucleon -nucleon correlation on symmetry energy Chang Xu and Bao-An Li, ar. Xiv: 1104. 2075

Symmetry energy Esym(ρ) and its density slope L(ρ) at arbitrary density based on the Hugenholtz-Van Hove (HVH) theoremtheorem Single-particle potential Fermi momentum Kinetic energy Energy density C. Xu, B. A. Li and L. W. Chen and C. M. Ko, ar. Xiv: 1004. 4403, NPA (2011) in press.

Symmetry potential at saturation density from global nucleon optical potentials Systematics based on world data accumulated since 1969: (1) Single particle energy levels from pick-up and stripping reaction (2) Neutron and proton scattering on the same target at about the same energy (3) Proton scattering on isotopes of the same element (4) (p, n) charge exchange reactions

Constraining the symmetry energy near saturation density using global nucleon optical potentials C. Xu, B. A. Li and L. W. Chen, PRC 82, 054606 (2010).

Theoretical predictions on the correlation between Esym(ρ0) and L(ρ0) using constraints on optical potentials Under the condition that they Agree with the EOS of PNM at low densities pewdicted by A. Schwenk and C. Pethick, PRL 95 (2005) 160401 Will Newton et al. (2011) Chen et al. Steiner

Constraints extracted from data using various models Iso. Diff & double n/p (Im. QMD, 2009), GOP: global optical potentials (Lane potentials) C. Xu, B. A. Li and L. W. Chen, PRC 82, 054606 (2010) M. B. Tsang et al. , PRL 92, 122701 (2009). Iso Diff. (IBUU 04, 2005), L. W. Chen et al. , PRL 94, 32701 (2005) IAS+LDM (2009), Danielewicz and J. Lee, NPA 818, 36 (2009) PDR (2010) of 68 Ni and 132 Sn, A. Carbone et al. , PRC 81, 041301 (2010). PDR (2007) in 208 Pb Land/GSI, PRC 76, 051603 (2007) SHF+N-skin of Sn isotopes, L. W. Chen et al. , PRC 82, 024301 (2010) Isoscaling (2007), D. Shetty et al. PRC 76, 024606 (2007) DM+N-Skin (2009): M. Centelles et al. , PRL 102, 122502 (2009) Esym(ρ0)≈ 31 ± 4 Me. V TF+Nucl. Mass (1996), Myers and Swiatecki, NPA 601, 141 (1996) L≈ 60 ± 23 Me. V

Some basic issues on symmetry energy at low densities neutron +proton uniform matter at density ρ and isospin asymmetry What is the isospin-dependence of the EOS of clustered matter? as density decreases Invariance of nuclear interaction under n-p exchange, for uniform matter

Isospin dependence of the EOS of clustered matter Quantum statistical model S-matrix approach S. Typel, G. Ropke, T. Klahn, D. Blaschke and H. H. Wolter, PRC 81, 015803 (2010) J. N. De, S. K. Samaddar, PRC 78, 065204 (2008) S. K. Samaddar, J. N. De, X. Vinas and M. Centelles, PRC 80, 035803 (2009) Uniform matter T=4 Me. V n=0. 001 fm-3 e. V M 2 T= Clustered matter The anharmonic behavior depends on whether all mirror nuclei are included in pairs

What “symmetry energies’’ are we talking about for clustered matter? Even if we know the answer, at what densities? Normal or really low? (1) Isospin-independent “symmetry energy-1” For the sake of getting the traditionally defined symmetry energy and compare it with the one for uniform matter, (2) Isospin-independent “symmetry energy-2” (3) Isospin-dependent “symmetry energy” by forcing the EOS to be quadratic

Pairing effects on symmetry energy at low densities Considering nn and pp pairing in T=1 only using 3 kinds of pairing intereactions E. Khan, J. Margueron, G. Colò, K. Hagino, and H. Sagawa, PRC 82, 024322 (2010)

Effects of n-p pairing on symmetry energy at low densities Yuan Tian and Bao-An Li (2011) using separable Paris potential To my best knowledge, Nobody has considered both clusters and pairing at low densities simultaneously yet

Super-uncertainty of Symmetry Energy at Supra-saturation Densities Z. G. Xiao, Bao-An Li, L. W. Chen, G. C. Yong and M. Zhang, PRL 102, 062502 (2009) Old issues: (1) Model dependence because of the complexity of transport models, inconsistent and diverse input mean-field and in-medium elementary hadron-hadron cross sections (2) Few known probes that are clean and strongly sensitive to the symmetry energy which is a small percent of the total potential energy especially at high densities

A new issue: magnetic effects on the pion ratio In off-central Au+Au collisions at RHIC, D. Kharzeev, L. Mc. Lerran and H. Warringa, NPA 803: 227 (2008) In sub-Coulomb barrier U+U collisions, the magnetic field B is on the order of 1014 G J. Rafelski and B. Muller, PRL 36, 517 (1976)

*1. 44 1013 G Provides the possibility to study properties of dense matter under strong magnetic field as in neutron stars Ou Li and Bao-An Li (2011)

Beam energy and impact parameter dependence of magnetic field created in heavy-ion collisions

No magnetic effect on nucleon observables because the Lorentz force is very small compared to nuclear force Nuclear force over magnetic force

Significant Magnetic effects on pion ratio Empirically, no nuclear mean-field on pions in most transport models and the pion cascade is sufficient to describe available data Theoretically, pion mean-field or dispersion relation is very uncertain Pions are light and moving fast, they thus feel stronger Lorentz force

No magnetic field effect considered in neither model calculations nor data analysis (extrapolating to very forward and backward angles to obtain the total multiplicity) W. Reisdorf et al. , NPA 781 (2007) 459

Conclusion and Perspectives • Conclusion: No! • Perspectives: a lot! Thank you!