NSF Award
2412792
Almost all the mass of atoms resides in the nucleons (protons and neutrons) that make up the corresponding atomic nucleus. Nucleons are not elementary particles but rather complicated bound states of quarks and gluons (collectively denoted as partons), whose interaction is described by quantum chromodynamics (QCD). The parton structure of the nucleon is encoded in different parton distributions and quark-gluon correlations. Both parton distributions and quark-gluon correlations can, in principle, be studied through high-energy (hard) scattering processes at particle accelerators, including the future Electron-Ion Collider in the USA. However, for quark-gluon correlations this is very difficult, and therefore these quantities are presently largely unexplored. The first goal of the project is to develop and apply an improved theoretical framework for extracting the nucleon transversity, one of the least explored parton distributions, from data on high-energy processes. Along with that goes a state-of-the-art extraction of the tensor charge, one of the fundamental properties of the nucleon. The second goal is to develop a formalism which allows for the calculation of quark-gluon correlations numerically in QCD, thus circumventing the lack of information from experiment. The project integrates research and teaching of graduate and undergraduate students, as well as educational outreach.<br/><br/>The work on the transversity parton distributions and the tensor charge extends our previous studies in this area. A special focus is on enhancing the QCD formalism for the analysis of data on di-hadron production by computing next-to-leading-order perturbative corrections. This framework then serves as a key ingredient of a novel extraction of the transversity and tensor charge of the nucleon, which uses all pertinent data on di-hadron (and single-hadron) production. A major goal of this study is the comparison of the nucleon tensor charge based on experimental data with benchmark results obtained from first-principles calculations in lattice-QCD. The study of the quark-gluon correlations exploits a new class of Euclidean parton correlators that can be computed in lattice-QCD. While these correlators do not directly provide the QCGs of interest, the two types of quantities can be related through calculations in perturbative QCD. Developing the required formalism, which presently is in its infancies, is a key objective of the project. Close interaction is foreseen with researchers performing numerical calculations in lattice-QCD, to ensure that the new theoretical framework can be readily put into practice.<br/><br/>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.
