Recoil Geometry Unmasks Gluon Saturation in Forward Z0 Production
Abstract
Gluon saturation produces characteristic transverse-momentum broadening in nuclei, but QCD radiation largely washes out this signature. We show that fiducial recoil subtraction turns detector acceptance into a transverse-momentum projector that unmasks the broadening in forward Z0 production. Subtracting the hadronic recoil measured in a chosen rapidity interval from the boson transverse momentum defines a residual momentum. At leading power, the radiative recoil in this interval cancels, while the residual momentum retains sensitivity to the small-x nuclear field. Combining a CGC description of the small-x target with soft-collinear effective theory (SCET) resummation for finite rapidity coverage, we find that a benchmark rapidity coverage |ηlab|<2.5 lowers the effective hard scale from MZ≃ 91.2 GeV to about 7.5 GeV of the Sudakov evolution. Increasing the saturation scale broadens the residual-momentum distribution and weakens recoil alignment, whereas wider coverage makes the proton--nucleus separation clearer in both observables. Detector geometry thus provides tunable control over perturbative recoil, enabling a probe of nonlinear small-x QCD.
Related
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BibTeX
@misc{li2026recoil,
title = {{Recoil Geometry Unmasks Gluon Saturation in Forward $Z^0$ Production}},
author = {Wanchen Li and Ding Yu Shao and Shu-Yi Wei and Jian Zhou},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.02356},
eprint = {2609.02356},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.02356},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Recoil Geometry Unmasks Gluon Saturation in Forward Z^0 Production
AU - Wanchen Li
AU - Ding Yu Shao
AU - Shu-Yi Wei
AU - Jian Zhou
PY - 2026
DA - 2026/09/02
PB - arXiv
DO - 10.48550/arxiv.2609.02356
UR - https://arxiv.org/abs/2609.02356
AB - Gluon saturation produces characteristic transverse-momentum broadening in nuclei, but QCD radiation largely washes out this signature. We show that fiducial recoil subtraction turns detector acceptance into a transverse-momentum projector that unmasks the broadening in forward Z^0 production. Subtracting the hadronic recoil measured in a chosen rapidity interval from the boson transverse momentum defines a residual momentum. At leading power, the radiative recoil in this interval cancels, while the residual momentum retains sensitivity to the small-x nuclear field. Combining a CGC description of the small-x target with soft-collinear effective theory (SCET) resummation for finite rapidity coverage, we find that a benchmark rapidity coverage |η^lab|<2.5 lowers the effective hard scale from M_Z≃ 91.2 GeV to about 7.5 GeV of the Sudakov evolution. Increasing the saturation scale broadens the residual-momentum distribution and weakens recoil alignment, whereas wider coverage makes the proton--nucleus separation clearer in both observables. Detector geometry thus provides tunable control over perturbative recoil, enabling a probe of nonlinear small-x QCD.
ER -