D. R. Green

Enhanced leading production of D+- and D*+- in 250-GeV pi+- - nucleon interactions

A leading charm meson is one with longitudinal momentum fraction, [ital x][sub [ital F]][gt]0, whose light quark (or antiquark) is of the same type as one of the quarks in the beam particles. We report on the production asymmetry, [ital A]=[[sigma](leading[minus][sigma](nonleading)]/[[sigma](leading)+[sigma](nonleading)] as a function of [ital x][sub [ital F]]. The data consist of 1500 fully reconstructed [ital D][sup [plus minus]] and [ital D][sup *[plus minus]] decays in Fermilab experiment E 769. We find a significant asymmetry for the production of charm quarks is not expected in perturbative quantum chromodynamics.

Atomic mass dependence ofΞ−andΞ¯+production in central 250 GeVπ−-nucleon interactions

We present the first measurement of the atomic mass dependence of central Ξ− and Ξ + production. It is measured using a sample of 22,459 Ξ−’s and Ξ + ’s produced in collisions between a 250 GeV π− beam and targets of beryllium, aluminum, copper, and tungsten. The relative cross sections are fit to theWe present the first measurement of the atomic mass dependence of central \Xi^- and \overline{\Xi}^+ production. It is measured using a sample of 22,459 \Xi^-s and \overline{\Xi}^+s produced in collisions between a 250 GeV \pi^- beam and targets of beryllium, aluminum, copper, and tungsten. The relative cross sections are fit to the two parameter function \sigma_0 A^\alpha, where A is the atomic mass. We measure \alpha = 0.924+-0.020+-0.025, for Feynman-x in the range -0.09