Nucleon-Number Dependence of Massive Hadron Pair Production in 400 Gev/c Proton-Nucleus Collisions

We have studied the nucleon-number (A) dependence in the production of hadron pairs, roughly back to back near 90(DEGREES) in the proton-nucleon center of momentum frame, by the interactions of 400 GeV/c protons with nuclear targets. The effective mass of hadron pairs we studied was in the range from 7.5 GeV/c('2) to 12.5 GeV/c('2). The motivation is to clarify the behaviour of hard scatterings of constituent quarks and gluons on the apparently cooperative nuclear effects, i.e. A('(alpha)) where (alpha) > 1. We have measured the mass, p(,T) and p(,out) dependence in order to understand the A-dependence for hadron pairs. Results are in qualitative agreement with theories of quarks and gluons (QCD) in which these constituents undergo multiple scattering in heavy nuclei before fragmenting into observable hadrons.