The equation of state of nuclear matter, which consists of neutrons and protons, has the term that depends on the difference between the neutron and proton densities. Determination of the term, the symmetry energy term, is quite important for nuclear physics as well as nuclear astrophysics. The symmetry energy is one of key ingredients to determine e.g. the radius and internal structure of a neutron star as well as supernova explosion dynamics. The first order density dependence, slope parameter, of the symmetry energy has a close correlation with the thickness of the neutron skin, which is a neutron rich layer that appears on the surface of heavy nuclei. We pick up three recent measurements on the neutron skin thickness of the ^<208>Pb nucleus by using each of weak, electromagnetic, and strong interactions, and report the present situation on the determination of the slope parameter.
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