2024

Dumitru, Adrian; Mäntysaari, Heikki; Tawabutr, Yossathorn

The recently revised small-𝑥 helicity evolution [J. High Energy Phys. 07 (2022) 095], resumming the double-logarithmic factor, 𝛼s⁢ln2⁡(1/𝑥), allows for the study of helicity distributions of quarks and gluons at small Bjorken 𝑥, corresponding to high center-of-mass energy. In this work, we calculate the moderate-𝑥 initial conditions in the regime, 𝛼s⁢ln2⁡(1/𝑥)∼1, for the small-𝑥 helicity evolution using a light-front valence quark model of the proton, which provides additional physical information about the target. The perturbative emission and absorption of a gluon by the valence quarks are also included. The results, given in Eqs. (35), provide a new set of initial conditions with a significantly reduced number of free parameters than conventional models [Phys. Rev. D 108, 114007 (2023)]. Consequently, the predictive power of small-𝑥 helicity evolution is expected to improve once the initial conditions from this work are incorporated.