Electromagnetic excitation of the double giant dipole resonance in ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$

The nuclear response of a medium-mass nucleus ${(}^{136}$Xe) to electromagnetic excitation in a near-relativistic heavy-ion collision was investigated in the ${\mathrm{reaction}}^{136}$Xe(0.7A GeV)+Pb. From an exclusive measurement of the neutron decay of the excited ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$ projectiles, strong excitations of giant resonances and, in particular, of the double isovector giant dipole resonance were identified. A resonance energy of 28.3±0.7 MeV, a width of 6.3±1.6 MeV, and a total cross section of 215±50 mb were found for the double giant dipole resonance.