  We report a parton distribution function (PDF) analysis of a complete set of
hadron scattering data, in which a color-octet fermion (such as a gluino of
supersymmetry) is incorporated as an extra parton constituent along with the
usual standard model constituents. The data set includes the most up-to-date
results from deep-inelastic scattering and from jet production in hadron
collisions. Another feature is the inclusion in the fit of data from
determinations of the strong coupling alpha_s(Q) at large and small values of
the hard scale Q. Our motivation is to determine the extent to which the global
PDF analysis may provide constraints on the new fermion, as a function of its
mass and alpha_s(M_Z), independent of assumptions such as the mechanism of
gluino decays. Based on this analysis, we find that gluino masses as low as 30
to 50 GeV may be compatible with the current hadronic data. Gluino masses below
15 GeV (25 GeV) are excluded if alpha_s(M_Z) varies freely (is equal to 0.118).
At the outset, stronger constraints had been anticipated from jet production
cross sections, but experimental systematic uncertainties, particularly in
normalization, reduce the discriminating power of these data.
