The scale $Q$ (left), and the fraction $x$ (right) of longitudinal momentum of the initial state partons of the hard process for photon production at midrapidity versus photon \pt\ for pp collisions at $\sqrt s = 7$ TeV, from a PYTHIA 8 simulation. The $x$ values of both partons are used here. The solid red line shows the median of the distribution in the parameters, while the red bands indicate the 68\ | |