Polarization effects of supersymmetric QCD in large-p/sub T/ direct photon production

The linear polarization P (approx. perpendicular minus parallel to the scattering plane) of large-p/sub T/ direct photons from unpolarized hadrons is considered. Contrary to standard QCD, where O(1) P vanishes, and to O(α/sub s/) P is very small and changes sign at angle theta/sub c.m./ = 900, it is shown that supersymmetric theories (involving scalar quarks and light gluinos), already to O(1), imply a substantial and positive P through a wide range of angles including theta/sub c.m./ = 900. As an illustration, P is calculated for p-barp→γ+X at collider energy (√s = 540 GeV) and p/sub T/> or approx. =30 GeV, with scalar-quark mass 20 GeV; we find Papprox.8--3 %, decreasing as p/sub T/ increases. The significance of the results as a test of the short-distance structure of supersymmetric QCD (valence part of the scalar-quark distribution) is discussed. The distribution of a top quark with mass 35 GeV is also determined, and its contribution to P is found to be very small