Speaker
Description
We discuss TMD factorisation at high energy (or small $x$), as emerging from the Color Glass Condensate (CGC) effective theory. We first present exemples of high-energy processes for which TMD factorisation was shown to hold at leading order in CGC perturbation theory. This includes back-to-back di-jet production in electron-nucleus ($eA$) and proton-nucleus ($pA$) collisions, single inclusive jet production in $eA$ deep inelastic scattering, and di-lepton production in $pA$ collisions. The relevant TMD PDFs describe small-$x$ partons in the nuclear target and include saturation effects associated with the high gluon occupancy. We then focus on the next-to-leading order corrections to selected processes. We show that these corrections preserve TMD factorisation and, moreover, they generate three types of evolution equations, as needed for the resummation of the large kinematical logarithms: the BK/JIMWLK equation for the rapidity logarithms, the DGLAP equation for the collinear ones, and the CSS equation for the Sudakov logarithms. We argue that TMD factorisation endowed with these three evolutions is well suited for studies of gluon saturation in hard processes at the Large Hadron Collider and the future Electron-Ion Collider.
