Speaker
Description
Double parton scattering (DPS) is the process in which one has two hard scatterings in an individual proton-proton collision. It can compete in rate with single scattering in certain kinematic regions and/or for certain processes, and reveals information on nucleon structure not accessible in single parton scattering: spatial, spin, and colour correlations between the partons inside the nucleon. The parton densities relevant to DPS are the double parton distributions (DPDs); at small distance between the two probed partons the DPDs can be computed in perturbation theory. I discuss this perturbative calculation at next-to-leading order – this is the key missing piece required for computations of DPS at NLO. The calculation for both the colour-singlet and colour-correlated DPDs will be covered – in the latter case, one encounters rapidity divergences, the treatment of which I will discuss in detail. We used two different regulator schemes, the δ regulator and Collins' regulator using space-like Wilson lines, and obtained identical results in both, providing a strong cross-check. To our knowledge this is the first application of the Collins regulator in a two-loop calculation.
