• Accepted Paper

Constraints on vectorlike top dipole interactions from top-associated photon measurements at the LHC

M. Sahraei, Y. Hosseini, and M. Mohammadi Najafabadi

Phys. Rev. D - Accepted 26 October, 2026

DOI: https://doi.org/10.1103/dbn4-jjh5

Abstract

Precision measurements of top-quark production with energetic photons provide a complementary probe of vector-like quarks with nonstandard radiative decays. We reinterpret the CMS differential tt‾γ measurement and the ATLAS fiducial tt‾γγ cross section to constrain the electromagnetic and chromomagnetic transition interactions of a charge-2/3 vector-like top partner, T. We consider effective interactions written in terms of physical fields after electroweak symmetry breaking, retaining only the decays T→tγ and T→tg. The CMS signal includes both the mixed (tγ)(tg) topology and double-radiative tt‾γγ events entering the exactly-one-photon fiducial region, while the ATLAS rate is interpreted using a signal-specific detector-response transfer factor. Signal uncertainties are included, and the interpretation is restricted point by point to the domain satisfying the EFT and narrow-width requirements. Denoting the electromagnetic and chromomagnetic transition coefficients by ctγ and ctg, respectively, we find that, for $c_{tg}=1.0\times10^{-5}~\GeV^{-1}$ and $m_T=500~\GeV$, the observed Run~2 exclusions at 95% confidence level extend down to $c_{t\gamma}\simeq4.7\times10^{-7}~\GeV^{-1}$ for CMS and $2.3\times10^{-6}~\GeV^{-1}$ for ATLAS within the valid domain. At $m_T=1000~\GeV$, the corresponding values are 2.1×10−6 and $8.5\times10^{-6}~\GeV^{-1}$. Projections to the HL-LHC indicate improved sensitivity to these radiative transition interactions. These results establish top-associated photon measurements as complementary probes of radiative top-partner interactions beyond searches targeting conventional decay modes.

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