We have measured the cross sections d(2)sigma/dP(T)deta for production of isolated direct photons in p (p) over bar collisions at two different center-of-mass energies, 1.8 TeV and 0.63 TeV, using the Collider Detector at Fermilab. The normalization of both data sets agrees with the predictions of quantum chromodynamics for a photon transverse momentum (P-T) of 25 GeV/c, but the shapes versus photon P-T do not. These shape differences lead to a significant disagreement in the ratio of cross sections in the scaling variable x(T)(=2P(T)/roots). This disagreement in the x(T) ratio is difficult to explain with conventional theoretical uncertainties such as scale dependence and parton distribution parametrizations. RI Lancaster, Mark/C-1693-2008; Vucinic, Dejan/C-2406-2008; Nomerotski, Andrei/A-5169-2010; Ruiz, Alberto/E-4473-2011; St.Denis, Richard/C-8997-2012; Prokoshin, Fedor/E-2795-2012; Chiarelli, Giorgio/E-8953-2012; Azzi, Patrizia/H-5404-2012
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