  This work presents a direct measurement of the $^{96}$Ru($p,
\gamma$)$^{97}$Rh cross section via a novel technique using a storage ring,
which opens opportunities for reaction measurements on unstable nuclei. A
proof-of-principle experiment was performed at the storage ring ESR at GSI in
Darmstadt, where circulating $^{96}$Ru ions interacted repeatedly with a
hydrogen target. The $^{96}$Ru($p, \gamma$)$^{97}$Rh cross section between 9
and 11 MeV has been determined using two independent normalization methods. As
key ingredients in Hauser-Feshbach calculations, the $\gamma$-ray strength
function as well as the level density model can be pinned down with the
measured ($p, \gamma$) cross section. Furthermore, the proton optical potential
can be optimized after the uncertainties from the $\gamma$-ray strength
function and the level density have been removed. As a result, a constrained
$^{96}$Ru($p, \gamma$)$^{97}$Rh reaction rate over a wide temperature range is
recommended for $p$-process network calculations.
