Density-dependence of nuclear symmetry energy

许 昌南京大学物理学院

2012. 4. 12-16

Collaborators: 任中洲 (NJU), 陈列文 (SJTU), 李宝安(TAMU)

Outline

1. Brief Introduction of Symmetry Energy

2. Theoretical Formulism (Esym and L)

3. Results and Discussion

4. Short Summary

Nuclear symmetry energy ------ a key issue in both nuclear physics and astrophysics

18

18

12

12

12

3

0 )) (, (( ) sn ymp

nn

p pE E E

symmetry energy

Energy per nucleon in symmetric nuclear matter

Energy per nucleon in asymmetric nuclear matter

Isospin asymmetry

1. Introduction

A.W. Steiner, M. Prakash, J.M. Lattimer and P.J. Ellis, Phys. Rep. 411, 325 (2005).

Isospin physicsIsospin physicsn/p n/p

isoscaling isoscaling

isotransportisotransport isodiffusionisodiffusion

t/t/33HeHe isofractionationisofractionation

KK++/K/K00

isocorrelation isocorrelation

ππ--//ππ++

inTerrestrial Labs

(QCD)(Effective Field Theory)

Recent progress:1 Experimentally, some constraints

on Esym at sub-saturation densities (ρ< ρ0) have been obtained recently from analyzing nuclear reaction data.

2 Esym at normal nuclear density is known to be around 30MeV from analyzing nuclear masses and other data.

3 At supra-saturation densities (ρ> ρ0) , however, the situation is much less clear because of the very limited data available.

BUU calculations…

2. Theoretical Formulism

• Starting from the Hugenholtz–Van Hove theorem that is a fundamental relation among the Fermi energy, the average energy per particle E and the pressure of the system P at the absolute temperature of zero.

The nucleon single-particle potentials can be expanded as a power series

isoscalar isovector

Lane potential:

2. Theoretical Formulism

Comparing the coefficient of each term then gives the symmetry energy of any order

Question:

• Nuclear Density Functional Theory (DFT) program at the Institute of Nuclear Theory in Seattle (2005) :

• http://www.int.washington.edu/PROGRAMS/dft.html

• Another goal is to understand connections between the symmetry energy and isoscalar and isovector mean fields?

• Symmetry energy: Kinetic energy part, isoscalar potential part, isovector potential part (most uncertain)

Xu et. al, Phys. Rev. C 82, 054607 (2010); Xu et. al, Nucl.Phys. A 865 (2011) 1Xu et. al, Phys. Rev. C 81, 064612 (2010)

BUU: The Momentum dependent Interaction (MDI)

L: its exact value is particularly important for determining several critical quantities, such as the size of the neutron skin in heavy nucleilocation of the neutron drip linecore-crust transition density and gravitational binding energy of neutron stars

The symmetry energy can be characterized by using the value of Esym(ρ0) and the slope parameter L

3.Symmetry energy and its slope at saturation density

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).

Iso Diff. (IBUU04, 2005),Iso Diff. (IBUU04, 2005),L.W. Chen et al., PRL94, 32701 (2005)L.W. Chen et al., PRL94, 32701 (2005)

IAS+LDM (2009),IAS+LDM (2009),Danielewicz and J. Lee, NPA818, 36 (2009)Danielewicz and J. Lee, NPA818, 36 (2009)

PDR (2007) in 208Pb Land/GSI, PRC76, 051603 (2007)

Constraints extracted from data using various modelsIso. Diff & double n/p (ImQMD, 2009), M. B. Tsang et al., PRL92, 122701 (2009).

GOP: global optical potentials (Lane potentials)C. Xu, B.A. Li and L.W. Chen, PRC 82, 054606 (2010)

PDR (2010) of 68Ni and 132Sn, A. Carbone et al., PRC81, 041301 (2010).

SHF+N-skin of Sn isotopes, L.W. Chen et al., PRC 82, 024301 (2010)

Isoscaling (2007), D.Shetty et al. PRC76, 024606 (2007)

DM+N-Skin (2009): M. Centelles et al., PRL102, 122502 (2009)

TF+Nucl. Mass (1996), Myers and Swiatecki, NPA601, 141 (1996)

Symmetry energy and its slope at saturation density

Symmetry energy at supra-saturation density

• Some indications of a supersoft Esym at high densities have been obtained from analyzing the π+/π− ratio data.

• Experiments have now been planned to investigate the high-density behavior of the Esym at the CSR in China, GSI in Germany, MSU in the United States, and RIKEN in Japan.

• Possible physical origins of the very uncertain Esym at supra-saturation densities?

U0: relatively well determined

Usym measures the explicit isospin dependence of the nuclear strong interaction, namely, if the effectiveinteractions are the same in the isosinglet and isotriplet channels, then the Usym = 0

However, the Usym is very poorly known especially at high momenta.

0 1 0

sym 1 0

3 1U

2 4 41 1

U2 4 4

n pT T

n pT T

U Uu u

U Uu u

Effects of the spin-isospin dependent three-body force

Effects of the in-medium short range tensor force and nucleon correlation

Effects of the spin-isospin dependent three-body force

The symmetry energy obtained with different spin dependence x0 and density dependence α in the three-body force (Gogny force)

Effects of the in-medium short-range tensor force

The pion and rho

meson exchanges

tensor forces

We use the Brown-Rho Scaling (BRS)

for the in-medium rho meson mass

The symmetry energy with different values of the BRS parameter αBR= 0, 0.05, 0.10, 0.15, 0.20 using different values for the tensor correlation parameter.

4. Summary

1. General expressions are derived for Esym and L by using the HVH theorem.

2. Esym and L at normal density: extracted values from the global optical potential

3. The reason why the Esym and L at supra saturation density so uncertain: isospin-dependence of the three-body force, tensor force, nucleon-nucleon correlation.

Thanks!

References

• N. M. Hugenholtz and L. Van Hove, Physica 24, 363 (1958)

• C. Xu, B. A. Li, L. W. Chen, and C. M. Ko, ArXiv:1004.4403.

• K. A. Brueckner and J. Dabrowski, Phys. Rev. 134, B722 (1964).

• J. Decharge and D. Gogny, Phys. Rev. C 21, 1568 (1980).

• M. L. Ristig, W. J. Louw, and J. W. Clark, Phys. Rev.C 3, 1504 (1971).