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Yiyu Zhou, Physics - Final Oral Dissertation Defense
 Zoom link is available upon request. Please email [[w|evwilk,Ellie]]

Title: “Proton Spin Structure from Simultaneous Monte Carlo Global QCD Analysis”

Abstract: In quantum chromodynamics (QCD), parton distribution functions (PDFs) encode the momentum and helicity distributions of quarks and gluons inside a proton. Being inherently nonperturbative, PDFs have to be extracted from unpolarized and polarized lepton-hadron and hadron-hadron scattering data. In particular, experiments that measure unpolarized and polarized jet observables can provide insight into the momentum and helicity distributions of gluons.
In this thesis, we perform the first simultaneous extraction of the spin-averaged and spin-dependent (or helicity) PDFs from deep-inelastic scattering, Drell-Yan and single jet observables, within the Monte Carlo global QCD analysis framework developed by the Jefferson Lab Angular Momentum (JAM) Collaboration. The results from this work indicate that the gluon helicity distributions depend rather strongly on the theory assumptions on which the global analysis is based.
    As an application of the new JAM analysis, we perform an impact study for future Electron-Ion Collider (EIC) data with parity-conserving and parity-violating polarization asymmetries on quark and gluon helicity distributions in the proton. The extrapolation of structure functions from the current data is studied for the first time in the context of the impact study. Theory assumptions, such as SU(2) and SU(3) flavor symmetries, are also studied to give a more thorough understanding of the impact of EIC pseudodata on proton spin structure.

Bio:  Yiyu Zhou was born in1992 in Xingping, Shaanxi Province, P.R. China. Since his youth, he has always been curious about many things related to science and math. His formal education began in 1999 at Shaanchai Elementary School in Xingping, Shaanxi Province. After completing primary and secondary education in Xingping, he was admitted into the Xi'an Jiaotong University in Xi'an, Shaanxi Province. His major was Biology Engineering at first, but later transferred to the Physics Elite Class in the School of Science. He won the national first class scholarship in 2012 and the undergraduate research scholarship in 2014. Dissatisfied with college-level physics, he entered William & Mary in Fall 2015. In 2017, he joined the High Energy Theory Group to work with Prof. Joshua Erlich on emergent gravity and supersymmetry. In November 2018, he decided to work on hadron physics with Prof. Wally Melnitchouk at Jefferson Lab on extracting parton helicity distribution in protons from experimental data. After graduation, he will continue his research in QCD in a joint postdoc position at South China Normal University and UCLA.