A New Look At Small-$x$ Helicity Phenomenology: Investigating Uncertainties And The Impact Of Polarized Proton-proton Data

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Main Author: Baldonado, Nicholas
Format: Preprint
Published: 2025
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author Baldonado, Nicholas
author_facet Baldonado, Nicholas
contents This dissertation highlights the contributions I have made to the field of theoretical nuclear physics, specifically in high-energy Quantum Chromodynamics (QCD). High-energy QCD is a robust subject and my research is refined to the sub-field of small-$x$ spin physics; small-$x$ physics is characterized by high-energy and density collisions and is well-suited for the Color Glass Condensate (CGC) effective field theory. Small-$x$ spin physics takes the ultra-relativistic description of high-energy QCD and gives special attention to spin-dependent interactions suppressed by powers of the center-of-mass energy. My expertise lies in exploring the theory and phenomenology relating to the KPS-CTT small-$x$ helicity evolution equations, a rubric that allows one to make predictions of the quarks' and gluons' distributions of spin at small-$x$. These predictions are heavily influenced by the initial conditions of the evolution, and the initial conditions are determined through analyses of world polarized data. My contributions focus on Bayesian parameter analysis, numerical and analytical calculations to discretize and cross-check the evolution equations, and the incorporation of a new observable into the pool of analyzed data. The results of such work show that the net amount of spin from quarks and gluons in the small-$x$ regime is predicted to be negative and/or potentially small; an analysis of polarized deep-inelastic scattering (DIS) and semi-inclusive DIS (SIDIS) data resulted in a net small-$x$ spin prediction that can be large and negative, but new results with the inclusion of data for single-inclusive jet production in polarized proton-proton ($pp$) collisions now estimate that the net amount of parton spin at small $x$ is small, with 1-$σ$ uncertainty that spans zero.
format Preprint
id arxiv_https___arxiv_org_abs_2504_16284
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle A New Look At Small-$x$ Helicity Phenomenology: Investigating Uncertainties And The Impact Of Polarized Proton-proton Data
Baldonado, Nicholas
High Energy Physics - Phenomenology
High Energy Physics - Theory
Nuclear Theory
This dissertation highlights the contributions I have made to the field of theoretical nuclear physics, specifically in high-energy Quantum Chromodynamics (QCD). High-energy QCD is a robust subject and my research is refined to the sub-field of small-$x$ spin physics; small-$x$ physics is characterized by high-energy and density collisions and is well-suited for the Color Glass Condensate (CGC) effective field theory. Small-$x$ spin physics takes the ultra-relativistic description of high-energy QCD and gives special attention to spin-dependent interactions suppressed by powers of the center-of-mass energy. My expertise lies in exploring the theory and phenomenology relating to the KPS-CTT small-$x$ helicity evolution equations, a rubric that allows one to make predictions of the quarks' and gluons' distributions of spin at small-$x$. These predictions are heavily influenced by the initial conditions of the evolution, and the initial conditions are determined through analyses of world polarized data. My contributions focus on Bayesian parameter analysis, numerical and analytical calculations to discretize and cross-check the evolution equations, and the incorporation of a new observable into the pool of analyzed data. The results of such work show that the net amount of spin from quarks and gluons in the small-$x$ regime is predicted to be negative and/or potentially small; an analysis of polarized deep-inelastic scattering (DIS) and semi-inclusive DIS (SIDIS) data resulted in a net small-$x$ spin prediction that can be large and negative, but new results with the inclusion of data for single-inclusive jet production in polarized proton-proton ($pp$) collisions now estimate that the net amount of parton spin at small $x$ is small, with 1-$σ$ uncertainty that spans zero.
title A New Look At Small-$x$ Helicity Phenomenology: Investigating Uncertainties And The Impact Of Polarized Proton-proton Data
topic High Energy Physics - Phenomenology
High Energy Physics - Theory
Nuclear Theory
url https://arxiv.org/abs/2504.16284