Precision in Drell Yan Lepton pair production at hadron colliders

Abstract

Over the last decade and given the impressive agreement between the Standard Model (SM) and the LHC experiments, particle physics has progressively become a precision science. In this scenario, where both SM and Beyond the Standard Model (BSM) physics must be tested through small deviations between theory and experiment, Drell Yan lepton pair production happens to gather the important properties of a precision observable. As the experimental determination for Drell Yan reaches the percent level, the study of this mechanism works both as an important testground for the Standard Model and as a way to evaluate alternative BSM theories, as well. Therefore, theory must be ready for this appointment by producing equally accurate instruments to correctly interpret the available high-precision data. One of the ways to access the Drell Yan mechanism is the inclusive cross-section. In this sense, in the first part of this work we complete the set of NNLO initial state corrections to the neutral current contributions to Drell Yan lepton pair production. We add both the mixed QCD⊗QED and the NNLO QED terms to the perturbative expansion of the production of a Z boson in hadronic collisions. Specifically, we obtain these corrections by exploiting the resemblance between the abelian part of QCD and the EW f f γ vertex to develop a suitable abelianisation procedure to extract the mixed order O(αsα) and even the pure electromagnetic O(α 2) results. Furthermore, in order to offer an integral description of the mechanism, we dig deeper and focus on the fully exclusive calculation of the mixed QCD⊗QED correction terms. In order to achieve this goal, we extend the qT -subtraction method, originally developed to address pure QCD corrections, to apply it to the calculation of the mixed NNLO contributions. We present the explicit expressions for the subtraction term and the hard factor, therefore providing all the ingredients needed for the application of the formalism up to O(αsα). We compute the mixed QCD⊗QED corrections and study the phenomenological impact at the level of kinematical distributions. Our exclusive computation was implemented within a parton level Monte Carlo code, which allows the user to apply arbitrary kinematical cuts on the final-state leptons and to compute the specified distributions in the form of bin histograms. The kinematical dependence of the full differential calculation, together with the magnitude of the inclusive result, were shown to be relevant and highly non trivial at the LHC energies.