Speaker: Joerg Raufeisen (Physics Division)

What can we learn about gluon saturation from heavy quark hadroproduction?

At very small Bjorken x, the linear QCD evolution equations predict a steep rise of the gluon distribution inside a proton, which will eventually violate unitarity. It is therefore expected that nonlinear corrections to the Altarelli-Parisi equations will slow down the growth of the gluon structure function, leading to parton saturation. However, despite many efforts, there is still no undisputable experimental evidence for gluon saturation. In this talk, I shall argue that hadroproduction of open charm and bottom may allow one to study saturation, because this process directly probes the gluon density of the colliding hadrons. I present the color dipole formulation of heavy quark production, which provides a convenient theoretical framework for the description of saturation effects. I also show numerical results for the cross section of heavy quark production in pp, pA and AA collisions at high energies, and I discuss possibilities to identify parton saturation in this process.