Speaker
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.
