The 208Pb(p,nγpˉ) 207Pb reaction at a beam energy of
30 MeV has been used to excite the anti-analog of the giant dipole resonance
(AGDR) and to measure its γ-decay to the isobaric analog state in
coincidence with proton decay of IAS. The energy of the transition has also
been calculated with the self-consistent relativistic random-phase
approximation (RRPA), and found to be linearly correlated to the predicted
value of the neutron-skin thickness (ΔRpn). By comparing the
theoretical results with the measured transition energy, the value of 0.190
± 0.028 fm has been determined for ΔRpn of 208Pb, in
agreement with previous experimental results. The AGDR excitation energy has
also been used to calculate the symmetry energy at saturation (J=32.7±0.6
MeV) and the slope of the symmetry energy (L=49.7±4.4 MeV), resulting in
more stringent constraints than most of the previous studies.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1205.232