Excitation function of giant resonances as doorway states in the 12C(p, p′)12C1 reaction between 19 and 23 MeV

Differential cross section and analyzing power angular distributions for the elastic scattering and inelastic scattering to the 2⁺ state at 4.44 MeV and the 1⁺ state at 12.7 MeV have been measured at incident proton energies varying from 19.15 to 23.34 MeV in 200 keV steps. Elastic scattering data are analyzed using an averaged optical model. Coupled-channel calculations reproduce roughly the 2⁺ data. The rapid variation of the data concerning the 1⁺ state is explained by virtual excitation of giant resonances. For each value of the incident energy, the coupling strength for each resonance is found by fitting the experimental angular distributions. The analysis assuming a weak coupling in the compound system gave a satisfactory fit to the cross section but a poor reproduction of the analyzing power. The assumption of a strong coupling in the ¹³N system allowed a good fit of all data. The angular distributions are dominated by the E1 resonance, whose $\text{1}\text{2}{}^{\mathrm{+}}$ component exhausting more than 37 % of the energy weighted sum rule, explains the isotropy of the cross section below 22 MeV. A $\text{7}\text{2}{}^{\mathrm{+}}$ resonance (15 % EWSR) is located at 19.9 MeV. The $\text{5}\text{2}{}^{\mathrm{?}}$ resonance with its maxima at 20.2 and 21.4 MeV, exhausts about 18 % of the sum rule, which is in good agreement with the results of previous works.