Physics Events
[PAST EVENT] Jacob James Ethier: Physics Dissertation Defense
Jacob James Ethier, Final Oral Examination for the Ph.D., Title: "Proton Spin Structure from Monte Carlo Global QCD Analyses."
Abstract: Although significant progress has been made in recent years to understand the composition of the proton's spin from its constituent quarks and gluons, a complete picture has yet to emerge. Such information is encoded in spin-dependent parton distribution functions (PDFs) that, as a consequence of being inherently non-perturbative, must be extracted through global QCD analyses of polarized lepton-proton and proton-proton collisions. Experiments that measure a final state hadron from these reactions are particularly useful for separating the individual quark and anti-quark polarizations, but require knowledge of parton-to-hadron fragmentation functions (FFs) to describe theoretically.
Recently, a series of global QCD fits were performed by the Jefferson Lab Angular Momentum (JAM) Collaboration to determine the spin PDFs and FFs from deep inelastic scattering (DIS), semi-inclusive DIS, and single inclusive electron-positron annihilation observables. While previous global QCD studies typically used a single chi-squared minimization procedure, the JAM collaboration applies a robust Monte Carlo fitting methodology to extract the central values and uncertainties of the relevant distributions. In this talk, I will discuss these JAM Monte Carlo analyses, including a first ever simultaneous fit of the spin PDFs and FFs, and their implications on the proton spin structure.
Bio: Jacob Ethier was born in Connecticut, where he lived before moving to Florida with his family at the age of 14. There he attended Stetson University from 2009-2013, graduating with a B.S. in physics and minor in mathematics. He entered the physics graduate program at William & Mary in August 2013, and has since been studying proton spin structure at the nearby Jefferson Lab with his advisor Wally Melnitchouk. After graduation, he will be moving with his wife and children to Amsterdam where he will be starting a postdoctoral research position at NIKHEF, the Dutch National Institute for Subatomic Physics.