Isospin splitting of the giant dipole resonance inY89

The total cross section for the reaction ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}(\gamma ,\mathrm{p}){}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$ has been measured; the existence of the coherent $T_{>}$ state is clearly demonstrated. Using our ($\gamma$,p) and the available ($\gamma$,n) results, a strength ratio of the $T_{>}$ to $T_{<}$ component $\frac{S_{>}}{S_{<}}$ equal to 0.13-0.14 is obtained. By determining the cross sections for various proton decay channels, the escape ${\Gamma }^{\uparrow }$ and spreading ${\Gamma }^{\downarrow }$ widths for the $T_{>}$ resonance were deduced. The direct decay probability of the $T_{>}$ state has been found to be $\frac{{\Gamma }^{\uparrow }}{\Gamma }=0.17\mathrm{}\pm 0.03$.