Time: 2:30pm Thursday, July 6, 2017

Location: Room9409
Speaker: Dr. Xing Hongxi (邢宏喜), Northwestern University／Argonne National Laboratory

Title: On the precision frontier: high orders in high energy nuclear physics

Abstract: The precision of perturbative QCD calculations has been reached an impressive level to test the standard model in modern hadron colliders. However, high precision computations for processes in heavy ion collisions are still very limited to probe accurately the fundamental QCD structure of the nucleus, such limitations also exist in polarized hadron collisions to determine the proton spin structure. In this talk, we first present some of our recent theoretical developments on radiative higher-order corrections to parton multiple scattering in the medium. We demonstrate how QCD factorization holds at next-to-leading order for multiple parton scattering in cold nuclear matter including both dilute (large-x) and dense (small-x) system, and discuss its implication for the medium properties. We then show the application of N-jettiness subtraction scheme in performing higher-order computations for polarized scattering processes. This method allows for a completely differential description of the cross section to match the desired experimental measurements. In particular, we show the two loop calculations of the beam function for longitudinal polarized quarks in QCD perturbation theory.