Double Parton Scattering at the LHC and Beyond

Most of the work on improving theoretical predictions for proton-proton collisions has focussed on improving the description of the highest-energy "primary" parton-parton collision. However, additional parton-parton collisions can and do occur. The case in which we have two high-energy parton-parton collisions in an individual proton-proton collision is known as double parton scattering (DPS). This process can compete in rate with single scattering in certain kinematic regions and/or for certain processes, reveals new information on proton structure, and becomes more important as collider energy grows. The aim of this project is to develop tools to make predictions for DPS that are based, for the first time, on first principles QCD theory. A major component of this work will be the further development of the Monte Carlo simulation of DPS, dShower - for example, to include certain quantum correlation effects, hadronisation, and unequal scale processes. These tools will then be applied to make predictions for key LHC processes where DPS can play an important role, such as the same-sign WW, multiple heavy flavour and 4 jet production processes. An important goal in this study will be to find measurements where the predictions of the full QCD framework differ from those obtained by the simplified DPS models used previously - these differences will be caused by inter-parton correlations and QCD effects present only in the former, and are both intrinsically interesting to search for experimentally, as well as being important to know for the accurate description of DPS backgrounds to other searches. A final goal in this project will be to improve the nonperturbative modelling in DPS predictions, by combining all known information about the nonperturbative part of DPS arising from theoretical constraints, lattice calculations, and experiment.