In this work, I present a phenomenological search for light neutral spin-1 vector mediators in elastic electron-proton ($ep$) scattering using a two-photon-exchange (TPE)-consistent framework. A vector boson that couples to electrons and protons modifies the $\varepsilon$-independent part of the unpolarized reduced elastic cross section ${\sigma }_R(\varepsilon ,Q^2)$ through interference with the photon, producing a characteristic shift in the Rosenbluth intercept. Using the full set of available Rosenbluth separations and a TPE-corrected baseline constructed from the Borisyuk-Kobushkin parametrization, I extract the intercept deviation across all measured $Q^2$ values spanning $0.0155\le Q^2\le 5.5{\mathrm{GeV}}^2$ and perform a profile-likelihood analysis to determine mass-dependent limits on the effective vector coupling. The data show no evidence for a vector contribution over the vector mass $m_V$ range of 0.04–10 GeV, and the resulting one-sided 95% C.L. upper bounds reach the few $\times {10}^{-4}-{10}^{-3}$ level at low mediator masses, weakening to the ${10}^{-3}-{10}^{-2}$ level at larger $m_V$ as expected from propagator suppression. These results provide strict, model-independent constraints on light vector interactions in elastic $ep$ scattering once TPE effects are consistently included.

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• Particle interactions
• QCD in nuclear reactions
• Form factors