Radiative Signature of New Scalar Boson Decays in the $m_{\mathrm{\ell }\mathrm{\ell }\gamma }$ Spectrum at the LHC

We investigate the radiative decay $S\to W^{+}{W}^{-}\gamma$ in the context of the multi-lepton anomalies and recent indications of a narrow scalar resonance near $m_S=152\pm 1\text{ GeV}$ in the $\gamma \gamma$, $Z\gamma$, and $W^{+}{W}^{-}$ channels at the Large Hadron Collider. These excesses arise in final states containing leptons, missing transverse momentum, and associated $b$-jets, and motivate a search for a corresponding localized excess in the invariant-mass spectrum of the dilepton–photon system, $m_{\mathrm{\ell }\mathrm{\ell }\gamma }$, in events with associated $b$-jets. We use recent CMS measurements of the $t\bar{t}\gamma$ differential cross sections~\cite{CMS:2025zbe} to study the $m_{\mathrm{\ell }\mathrm{\ell }\gamma }$ spectrum and perform a search for a scalar-resonance contribution. A localized excess is observed, compatible with the scalar-resonance hypothesis, with a global significance of $2.7\sigma$ at $m_S=152\text{ GeV}$. This result provides additional support for the hypothesis of a narrow resonance. The ratio $\sigma (S\to W^{+}{W}^{-}\gamma )\mathrm{/}\sigma (S\to W^{+}{W}^{-})=(2.14\pm 0.77)$% is extracted. This value is compatible with an enhanced radiative contribution that could arise in scenarios beyond the Standard Model.