COMPARISON OF DIRECT GAMMA PRODUCTION IN (P)OVER-BAR-P AND PP REACTIONS AND DETERMINATION OF LAMBDA(4)(MS)UNDER-BAR AND THE GLUON STRUCTURE-FUNCTION

Direct photons were studied in both ppBAR and pp interactions at square-root s = 24.3 GeV in the transverse momentum range 4.1 - 6.1 GeV/c (0.34 < x(T) < 0.5) for the rapidity range -0.2 - 1.0. The experiment was performed using an internal hydrogen jet target in the CERN SppSBAR collider. Preliminary cross sections in ppBAR and pp are presented. The cross-section difference sigma(ppBAR --> gammaX) - sigma(pp --> gammaX) has been measured and is compared to theoretical predictions. A preliminary determination of LAMBDA(4)/MS and of the gluon structure function is obtained.