23–25 Jun 2025
Physics and Astronomy Building
US/Pacific timezone

Small-$x$ Helicity Evolution: First Study on the Impact of Polarized $pp$ Scattering Data

25 Jun 2025, 11:10
25m
4-330 (Physics and Astronomy Building)

4-330

Physics and Astronomy Building

Speaker

Nicholas Baldonado (New Mexico State University)

Description

We perform a phenomenological study of helicity-dependent parton distribution functions (hPDFs) using the KPS-CTT small-$x$ helicity evolution equations. Specifically, this new work presents the first study of the influence of polarized proton-proton ($pp$) scattering data whilst simultaneously analyzing inclusive and semi-inclusive deep-inelastic scattering data, all at $x < 0.1$. Polarized $pp$ data in this analysis is limited to double-longitudinal spin asymmetries in single-inclusive jet production, for which we approximate it via the polarized small-$x$ pure-glue calculation of $pp\to gX$. We use a variant of the large-$N_c$ evolution equations by taking the large-$N_c\&N_f$ KPS-CTT evolution equations and setting $N_f = 0$ to replicate a pure-glue limit that retains external quark flavor dependence for the spinor field operators. We observe that the $pp$ data have a substantial impact on the helicity PDFs at small $x$, leading to reduced uncertainties and an updated total quark and gluon helicity contribution to the proton for $x < 0.1$ of $-0.04 \pm 0.23$. Comparing our analysis with a recent JAM analysis of world polarized data, including data at $x > 0.1$, we estimate a total parton helicity contribution for $x > 10^{-7}$ of between 0.02 and 0.51.

Authors

Andrey Tarasov (North Carolina State University) Dr Daniel Adamiak (Jefferson Lab) Daniel Pitonyak (Lebanon Valley College) Matthew Sievert (New Mexico State University) Dr Ming Li (The Ohio State University) Nicholas Baldonado (New Mexico State University) Nobuo Sato Wally Melnitchouk (Jefferson Lab) Yossathorn Tawabutr (University of Jyväskylä) Prof. Yuri Kovchegov

Presentation materials