New Probe of Line Broadening with Resolvable Fine Structure: The "Off-Diagonal Strength Function"

A recently developed technique enables one to measure the relative sign of inelastic proton-channel amplitudes of resonances. Using this we have measured signs of 32 fine-structure levels in the vicinity of the ${\frac{3}{2}}^{-}$ analog state seen in the reaction ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$+$p$ at $E_p=2.6\mathrm{}$ MeV. Thereby we construct a new type of datum, "the off-diagonal strength function," and compare this with the prediction made by the theory of analog-state broadening. This prediction involves no unknown parameters, and so the degree of fit provides an excellent test of the theory.