Measurement of Neutral Pion, Eta, and Direct Photon Production at High Transverse Momentum.

We have measured the high-p(,T) inclusive cross sections for (pi)('0) and (eta) production near 90(DEGREES) in the center of mass in 200 GeV/c (pi)('+) and proton collisions with beryllium, carbon, and aluminum targets. The cross section for both (pi)('0) and (eta) mesons rises with increasing nucleon number (A) of the target nucleus as A('(alpha)), with (alpha) > 1. We observe that the ratio for the (pi)('0) yield in pA collisions to that in (pi)('+)A collisions decreases with increasing p(,T). Also, we have measured the inclusive production of direct photons in the p(,T) range 2.1-5.0 GeV/c for the same interactions. We observe a significant yield of direct photons in pC and (pi)('+)C collisions for p(,T) > 2.5 GeV/c.