  In this paper we present a calculation of the $\gamma+j$ process at
next-to-next-to-leading order (NNLO) in QCD and compare the resulting
predictions to 8 TeV CMS data. We find good agreement with the shape of the
photon $p_T$ spectrum, particularly after the inclusion of additional
electroweak corrections, but there is a tension between the overall
normalization of the theoretical prediction and the measurement. We use our
results to compute the ratio of $Z(\to \ell^+\ell^-)+j$ to $\gamma+j$ events as
a function of the vector boson transverse momentum at NNLO, a quantity that is
used to normalize $Z(\rightarrow\nu\overline{\nu}) +j$ backgrounds in searches
for dark matter and supersymmetry. Our NNLO calculation significantly reduces
the theoretical uncertainty on this ratio, thus boosting its power for future
searches of new physics.
