Nucleon Structure and Hadronization Beyond the Collinear Leading Twist Parton Model

New Mexico State University, Las Cruces NM

Investigators

Abstract

It has been a long-standing question in nuclear physics of how the nucleon, the main building block of the matter that we are made of, is built from fundamental strongly-interacting elementary particles, the quarks and gluons. This project will address this question by studying correlations and 3-dimensional momentum distributions of quarks and gluons in the nucleon. To this end experimentally measurable observables are theoretically analyzed for nuclear reactions that can be realized at US-based facilities like the Jefferson Laboratory (JLab), the Relativistic Heavy Ion Collider (RHIC), and the future Electron-Ion Collider (EIC), as well as other facilities worldwide. The underlying microscopic theory on which this research is based is Quantum Chromodynamics (QCD). Several observables that are of interest for this project need spin polarization of the beam or the target, or even the produced final state particles. The theoretical analyses of those spin observables require methods and precision calculations that go beyond the common standard theoretical approaches for unpolarized nuclear reactions. The PI will mentor graduate students and include an undergraduate student in this research program. The main goal of this project is a theoretical investigation of the nucleon structure as well as parton fragmentation within perturbative QCD. It is intended to study observables of high-energy nuclear processes beyond the standard leading twist collinear factorization approach. The focus is on two key areas: 1) Transverse spin effects in single-inclusive nuclear processes within the collinear twist-3 formalism. 2) Transverse momentum dependent gluon distributions in polarized and unpolarized proton collisions. The outcome of these studies will have direct impact for experimental programs at JLab, RHIC, the Large Hadron Collider (LHC), and a future EIC. The main thrusts of the project are: i) Theoretical analyses of transverse spin-polarized observables in single-inclusive nuclear reactions in the framework of collinear twist-3 formalism: The goal is to perform next-to-leading (NLO) calculations for transverse-spin observables and to study the scale dependence of three-parton correlation functions. Furthermore, the PI will investigate the feasibility of photonic final state in lepton-nucleon collisions at JLab and EIC; ii) Exploration of the gluonic substructure of the nucleon within Transverse Momentum Dependent (TMD) factorization: TMD analyses of various gluon-induced spin observables in proton-proton collisions at RHIC with Heavy Quarkonia in the final state are considered including implementation of TMD evolution. 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.