Triply Differential Jet Cross Sections for Hadron Collisions at Order alpha_s^3 in QCD

We discuss cross sections for hadron + hadron to 2 jets + anything in which three jet variables are measured. Such cross sections are useful especially for determining parton distributions. We define a new cross section d sigma/dX_A dX_B d eta_* for which the perturbation theory is nicely behaved even in the kinematic regime where the parton distributions are probed at large momentum fractions. The cross section d\sigma/dE_{T1}\, d\eta_1\, d\eta_2, which has been used in the past, is not so well behaved in this region. We calculate these cross sections at order $\alpha_s^3$ in QCD.