Isospin mixing in theHe4giant dipole resonance

The addition of a new ($1^{-}$,0) level at 29 MeV excitation energy in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ to the level spectrum of Fiarman and Meyerhof leads to a calculated ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\gamma , p)$ to ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\gamma , n)$ cross section ratio of 1.67. The calculated ratio falls within the experimental range of 1.6-1.9 without utilizing charge-symmetry violating forces.