Probing the Moderate-to-Large-x Gluon Helicity with J/ψ Production at √s=GeV
Abstract
We investigate the longitudinal double-spin asymmetry, ALL, for color-singlet J/ψ production in longitudinally polarized pp collisions at √s≃27 GeV, relevant to the Spin Physics Detector at NICA. At these energies, gluon fusion probes moderate-to-large gluon momentum fractions, particularly at forward rapidity. We consider the leading-order color-singlet subprocess gg→ J/ψ+g within nonrelativistic QCD and calculate polarized and unpolarized cross sections using analytic partonic hard-scattering coefficients. The color-singlet long-distance matrix element cancels in ALL at this order. We study the transverse-momentum and rapidity dependence of the asymmetry using different polarized and unpolarized PDF combinations, including LO and NLO PDF inputs, while keeping the hard-scattering calculation at LO. Factorization- and renormalization-scale variations are examined, and PDF and scale uncertainties are combined. The asymmetry is positive and increases with transverse momentum in the kinematically stable region. Its magnitude and uncertainty become more sensitive to the polarized gluon distribution at moderate and large x, with substantial differences among PDF combinations at moderate and large transverse momentum. NLO PDF uncertainties are generally smaller than LO uncertainties in central regions, but this reduction is not uniform; PDF and scale uncertainties can both become sizable at high transverse momentum and forward rapidity. Differential measurements of ALL at SPD could therefore provide complementary constraints on gluon helicity in a relatively unexplored kinematic region. A complete NLO hard-scattering calculation is needed for precision predictions and a quantitative assessment of higher-order effects.
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BibTeX
@misc{sharma2026probing,
title = {{Probing the Moderate-to-Large-$x$ Gluon Helicity with $J/ψ$ Production at $\sqrts=\mathrmGeV$}},
author = {Shubham Sharma and Alexey Aparin and Satyajit Puhan and Narinder Kumar and Harleen Dahiya},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.30945},
eprint = {2605.30945},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.30945},
}
RIS
TY - UNPB
TI - Probing the Moderate-to-Large-x Gluon Helicity with J/ψ Production at √s=GeV
AU - Shubham Sharma
AU - Alexey Aparin
AU - Satyajit Puhan
AU - Narinder Kumar
AU - Harleen Dahiya
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2605.30945
UR - https://arxiv.org/abs/2605.30945
AB - We investigate the longitudinal double-spin asymmetry, A_LL, for color-singlet J/ψ production in longitudinally polarized pp collisions at √s≃27 GeV, relevant to the Spin Physics Detector at NICA. At these energies, gluon fusion probes moderate-to-large gluon momentum fractions, particularly at forward rapidity. We consider the leading-order color-singlet subprocess gg→ J/ψ+g within nonrelativistic QCD and calculate polarized and unpolarized cross sections using analytic partonic hard-scattering coefficients. The color-singlet long-distance matrix element cancels in A_LL at this order. We study the transverse-momentum and rapidity dependence of the asymmetry using different polarized and unpolarized PDF combinations, including LO and NLO PDF inputs, while keeping the hard-scattering calculation at LO. Factorization- and renormalization-scale variations are examined, and PDF and scale uncertainties are combined. The asymmetry is positive and increases with transverse momentum in the kinematically stable region. Its magnitude and uncertainty become more sensitive to the polarized gluon distribution at moderate and large x, with substantial differences among PDF combinations at moderate and large transverse momentum. NLO PDF uncertainties are generally smaller than LO uncertainties in central regions, but this reduction is not uniform; PDF and scale uncertainties can both become sizable at high transverse momentum and forward rapidity. Differential measurements of A_LL at SPD could therefore provide complementary constraints on gluon helicity in a relatively unexplored kinematic region. A complete NLO hard-scattering calculation is needed for precision predictions and a quantitative assessment of higher-order effects.
ER -