Distinguishing a pseudoscalar from a vector tt̅ resonance with top-quark spin correlations at the HL-LHC
Abstract
Top-quark spin correlations provide a direct probe of the quantum numbers of a resonance decaying to tt̅. We compare a CP-odd type-II two-Higgs-doublet-model pseudoscalar A with a spin-1 leptophobic topcolor Z' in the dilepton channel. The two hypotheses differ in the parton-level helicity correlation by Δchel≃0.43, nearly independently of mass, and neutrino-weighted reconstruction preserves this separation with an effective dilution factor of about 0.66. At 400 and 800 GeV, the pseudoscalar normalization is anchored to CMS HIG-22-013 coupling limits, while the Z' rate is matched to the pseudoscalar so that the comparison primarily tests spin structure. The leading-order tt̅-only projection gives expected separations of 2.27 and 2.74 standard deviations at 3000 fb−1. Equalizing the selected signal yields gives pure spin-shape separations of 1.86 and 2.70 standard deviations. Profiling a Gaussian-constrained Standard Model chel-shape nuisance gives 2.07 and 2.63 standard deviations for an optimistic sideband benchmark, or 1.67 and 2.26 for a weaker constraint. A local fixed-template extrapolation corresponds to five-standard-deviation discrimination at couplings about 22\% and 16\% above the reference values. A 1500 GeV g=1 point is shown separately. The reach is limited by the sub-percent signal fraction and control of the mass-dependent Standard Model spin shape, rather than by the intrinsic resonance-spin separation.
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BibTeX
@misc{bellagroudi2026distinguishing,
title = {{Distinguishing a pseudoscalar from a vector $t\bar t$ resonance with top-quark spin correlations at the HL-LHC}},
author = {Ahmed Bellagroudi and Farida Fassi},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11641},
eprint = {2609.11641},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.11641},
}
RIS
TY - UNPB
TI - Distinguishing a pseudoscalar from a vector tt̅ resonance with top-quark spin correlations at the HL-LHC
AU - Ahmed Bellagroudi
AU - Farida Fassi
PY - 2026
DA - 2026/09/10
PB - arXiv
DO - 10.48550/arxiv.2609.11641
UR - https://arxiv.org/abs/2609.11641
AB - Top-quark spin correlations provide a direct probe of the quantum numbers of a resonance decaying to tt̅. We compare a CP-odd type-II two-Higgs-doublet-model pseudoscalar A with a spin-1 leptophobic topcolor Z' in the dilepton channel. The two hypotheses differ in the parton-level helicity correlation by Δc_hel≃0.43, nearly independently of mass, and neutrino-weighted reconstruction preserves this separation with an effective dilution factor of about 0.66. At 400 and 800 GeV, the pseudoscalar normalization is anchored to CMS HIG-22-013 coupling limits, while the Z' rate is matched to the pseudoscalar so that the comparison primarily tests spin structure. The leading-order tt̅-only projection gives expected separations of 2.27 and 2.74 standard deviations at 3000 fb^−1. Equalizing the selected signal yields gives pure spin-shape separations of 1.86 and 2.70 standard deviations. Profiling a Gaussian-constrained Standard Model c_hel-shape nuisance gives 2.07 and 2.63 standard deviations for an optimistic sideband benchmark, or 1.67 and 2.26 for a weaker constraint. A local fixed-template extrapolation corresponds to five-standard-deviation discrimination at couplings about 22\% and 16\% above the reference values. A 1500 GeV g=1 point is shown separately. The reach is limited by the sub-percent signal fraction and control of the mass-dependent Standard Model spin shape, rather than by the intrinsic resonance-spin separation.
ER -