CGC-py: A Monte Carlo Event Generator for Gluon Saturation Physics
Abstract
We develop CGC-py, a Monte Carlo event generator for deep-inelastic scattering. It couples the full Color Glass Condensate (CGC) cross section for γ*p(A)→ qq̅+X to a Parton-Branching transverse-momentum-dependent backward initial-state shower, while \textsc{Pythia}~8 handles final-state radiation and hadronization. CGC-py retains the complete target-elastic and target-inelastic contributions without taking the back-to-back correlation limit, allowing single- and di-hadron observables to be generated consistently from the same event sample. We validate the generator through an analytic closure test of the single-inclusive quark spectrum and a comparison of charged-hadron spectra in ep collisions with H1 data, finding excellent agreement. The predicted nuclear modification factor ReAuh shows the expected saturation pattern: suppression at low pT* followed by a rise toward unity at higher pT*. A comparison with a \textsc{Pythia}~6 baseline, together with an xg-rescaling study, indicates that small-x CGC evolution and collinear DGLAP dynamics contribute comparably to the growth of the dihadron away-side width with energy. Genuine saturation-driven broadening emerges only at the highest energies considered. Within CGC-py, eAu collisions exhibit an enhanced away-side width and a suppressed back-to-back yield relative to ep collisions. These nuclear effects remain modest over EIC kinematics, motivating measurements at the most forward accessible kinematics and the use of complementary observables to maximize sensitivity to gluon saturation.
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BibTeX
@misc{duan2026cgcpy,
title = {{CGC-py: A Monte Carlo Event Generator for Gluon Saturation Physics}},
author = {Haowu Duan and Cong Yi and Si-Wei Dai and Shu-Yi Wei and Wenbin Zhao and Liang Zheng},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.03434},
eprint = {2609.03434},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.03434},
note = {CC0},
}
RIS
TY - UNPB
TI - CGC-py: A Monte Carlo Event Generator for Gluon Saturation Physics
AU - Haowu Duan
AU - Cong Yi
AU - Si-Wei Dai
AU - Shu-Yi Wei
AU - Wenbin Zhao
AU - Liang Zheng
PY - 2026
DA - 2026/09/03
PB - arXiv
DO - 10.48550/arxiv.2609.03434
UR - https://arxiv.org/abs/2609.03434
AB - We develop CGC-py, a Monte Carlo event generator for deep-inelastic scattering. It couples the full Color Glass Condensate (CGC) cross section for γ^*p(A)→ qq̅+X to a Parton-Branching transverse-momentum-dependent backward initial-state shower, while \textsc{Pythia}~8 handles final-state radiation and hadronization. CGC-py retains the complete target-elastic and target-inelastic contributions without taking the back-to-back correlation limit, allowing single- and di-hadron observables to be generated consistently from the same event sample. We validate the generator through an analytic closure test of the single-inclusive quark spectrum and a comparison of charged-hadron spectra in ep collisions with H1 data, finding excellent agreement. The predicted nuclear modification factor R_eAu^h shows the expected saturation pattern: suppression at low p_T^* followed by a rise toward unity at higher p_T^*. A comparison with a \textsc{Pythia}~6 baseline, together with an x_g-rescaling study, indicates that small-x CGC evolution and collinear DGLAP dynamics contribute comparably to the growth of the dihadron away-side width with energy. Genuine saturation-driven broadening emerges only at the highest energies considered. Within CGC-py, eAu collisions exhibit an enhanced away-side width and a suppressed back-to-back yield relative to ep collisions. These nuclear effects remain modest over EIC kinematics, motivating measurements at the most forward accessible kinematics and the use of complementary observables to maximize sensitivity to gluon saturation.
ER -