  We show that the Sudakov factor from the resummation of double logarithms
$\ln(s/k_T^2)$ contained in the distribution functions is responsible for the
$k_T$ smearing mechanism employed in the next-to-leading-order QCD
($\alpha\alpha_s^2$) calculations of direct photon production. $s$ is the
center-of-mass energy, and $k_T$ the transverse momentum carried by a parton in
a colliding hadron. This factor exhibits the appropriate $s$-dependent Gaussian
width in $k_T$, such that our predictions are in good agreement with
experimental data.
