We present a high-statistics, species-identified measurement of the W-to-Be per-nucleon cross-section ratio, RW/Be, for high-xt hadrons and high-τ h+h− pairs produced in p-A collisions at √s =38.8 GeV. The data extend to 0.62 in xt and 0.39 in √τ . For single hadrons, RW/Be peaks at pt≊5 GeV/c and decreases to ≊1 for mesons with pt>8 GeV/c. At fixed pt, RW/Be falls with √s . For symmetric pairs with √τ >0.28, RW/Be=0.84±0.02±0.07, suggesting a nuclear suppression of high-z fragmentation. RW/Be increases with pout, indicative of constituent multiple scattering.
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We present results on the production of hadrons in collisions of 400-GeV/c protons with beryllium, copper, and tungsten nuclei. The data cover the region from 5.6 to 8.0 GeV/c in the transverse momentum of the final-state hadron and from 73° to 102° in the proton-nucleon center-of-momentum frame production angle theta*. The restriction of the data to values of xT (xT=2pT/ √s ) greater than 0.4 enriches the sample with hard collisions of valence quarks. Asymmetries about theta*=90° reflect the presence of neutrons in the target nuclei. The variation of the atomic-weight dependence parameter α with production angle is discussed in the context of the phenomenology of nucleonic structure within nuclei. We also extrapolate our measurements to a ‘‘deuteron’’ target to minimize nuclear effects and compare the result to QCD calculations.
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