Precision Theory at the LHC: Strong Interaction Dynamics and New Physics Searches

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This award funds the research activity of Professor Marco Guzzi at Kennesaw State University. The CERN Large Hadron Collider (LHC) is the world's biggest and most powerful particle accelerator where high energy beams of protons, traveling at approximately the speed of light, collide. Accurate measurements from the LHC experiments brought high-energy physics to a new realm of precision that allows us to deepen our knowledge of the structure of matter and its elementary constituents and to shed light on possible new physics interactions. This field of research is vibrant and its rapid progress is of high importance for the national interest as it promotes advances of fundamental science that are crucial for new discoveries. Theoretical and experimental analyses at the unprecedented energies of the LHC demand precision. This is essential for meaningful comparisons between theory and experiment and a correct interpretation of the results. In his research, Professor Guzzi aims to calculate precise theoretical predictions and use efficient methods for phenomenology to improve our current knowledge of the structure of the proton and set stringent tests on the Standard Model of the elementary particles, as well as search for new particle signatures predicted by theories of new physics. The proposed research also has significant broader impacts: Professor Guzzi will involve students in his research, give public lectures on his research results, and develop new course curricula based on the results of his research.On the technical side, Professor Guzzi will use precise theory predictions for kinematic distributions of top-quark pairs produced at the LHC to reduce the uncertainties associated with parton distribution functions (PDF's). PDF's of the proton map out the longitudinal momentum distribution of its constituent quarks and gluons and they are a crucial limiting factor in the accuracy of theoretical predictions for many important observables at the LHC. A second part of the proposed project aims to improve the theory predictions for searches for extra neutral vector bosons at the LHC, generically referred to as Z' bosons. They differ from the Standard-Model Z boson by having different masses and couplings. With the improvements of the proton PDF's discussed above and with new precise measurements of dilepton pair production in Drell-Yan processes at LHC Run-II energies and luminosities, Professor Guzzi will study the parameter space of Z's of generic origin and will scrutinize a large number of new physics models. Finally, Professor Guzzi will determine with high precision the nonperturbative parameters of the transverse momentum dependent (TMD) distributions of the proton by using high-order perturbation theory and recent precise LHC measurements for Z-boson production in terms of a novel angular variable that has the advantage of being very sensitive to nonperturbative effects. TMD distributions represent the ultimate frontier of factorization theorems in QCD and allow us to have a unified framework in which to describe hadronic reactions in different energy regimes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.