Hard Scattering Processes in QCD

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Quantum Chromodynamics (QCD) is the microscopic theory of the strong interactions that allows us to understand how hadrons, such as the proton, neutron and pion, are formed. In turn, nucleons (protons and neutrons) make up more than 99% of the mass of the visible matter of the universe. Nucleons are composed of quarks and gluons (partons), the fundamental particles of QCD. The structure of the nucleon is studied using high-energy scattering processes at state-of-the-art experimental facilities in the USA and abroad. This project will provide theoretical guidance and help analyze experimental data generated at those experimental facilities. Furthermore, the PI will mentor graduate students and engage in outreach activities addressing high school students, teachers, and undergraduate students.The project will primarily concentrate on two topics in hadronic physics. First, a new fit of the transversity distribution will be performed for di-hadron production, which is generally considered a very clean channel. After a careful leading-order analysis, the transversity will be extracted in a collinear next-to-leading (NLO) order framework. This requires, in particular, the first-ever challenging NLO calculation of the relevant di-hadron observables in electron-positron annihilation, lepton-nucleon scattering and proton-proton collision. This study is expected to shed new light on the longstanding tension between information on the nucleon's transversity from experimental data on the one hand and from lattice QCD on the other. The second part of the project deals with partonic Wigner functions. For a number of reasons, partonic Wigner functions have attracted enormous interest over the last years. Despite their importance, presently no experimental information is available on these objects. The main focus will therefore be on observables for Wigner functions. This includes numerical estimates of observables, the calculation of higher-order corrections, and the search for new processes in which Wigner functions show up. Special attention will be paid to the question about how a future electron-ion collider (EIC) can further this research area.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.