RUI: Hadronic Structure from Spin Observables in pQCD

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The nucleus of an atom is made up of protons and neutrons, which are a part of a broader category of particles called hadrons. However, these hadrons are not a fundamental form of matter since they are composed of other particles, namely, quarks and gluons (collectively called partons). The partons form a dynamical system inside of hadrons that is governed by the strong nuclear force. A goal of nuclear physics research is to understand this internal structure through the interactions of these partons, the elementary pieces of visible matter. In particular, the analysis of high-energy collisions sensitive to an intrinsic property, called spin, of hadrons and/or partons is especially useful. These observables allow us to explore the 3-dimensional motion of partons inside of hadrons and how the proton's spin arises from its constituent partons. This research will give us better insight into these aspects of hadronic structure as well as support the science of the future Electron-Ion Collider to be built in the United States. Undergraduate students will be included in substantive parts of the project in order to foster the interests of young scientists in the subfield of nuclear physics and train them for future careers in research. This research project will further our knowledge of observables sensitive to parton intrinsic transverse motion and correlations, which allow for a 3-dimensional imaging of hadrons in momentum space. This includes performing a global analysis of data from various experiments sensitive to the spin of hadrons in order to extract the relevant functions, using an iterative Monte Carlo routine, that encode their internal structure. These functions will then be used to make predictions for upcoming measurements at the Relativistic Heavy Ion Collider (RHIC), Jefferson Lab's 12-GeV upgrade (JLab-12), and a future Electron-Ion Collider (EIC). Since a rigorous theoretical formalism is needed in order to interpret such experimental data, this project will also solidify the framework used in spin observables through higher-order calculations within quantum chromodynamics (QCD). The project will lastly investigate certain aspects of how the proton spin arises from its constituent partons by analyzing how much of this spin is due to partons that carry only a small fraction of the proton's momentum. The study will incorporate first principle results as input to the extraction of partonic functions that can be used to calculate their spin in this region.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.