Discovery Potential of Future Electron-Positron Colliders for a 95 GeV Scalar

Abstract

The Large Electron Positron collider observed an indication for a new Higgs boson with a mass around $95$\,GeV-$100$\,GeV in the process $e^{+}{e}^{-}\to Z^{\ast }\to ZS$ with $S\to b\bar{b}$. The interest in this excess re-emerged with the di-photon signature at $\approx$\,95\,GeV at the Large Hadron Collider. In fact, a combined global significance of $3.4\ddot{I}ƒ$ is obtained once $WW$ and $\ddot{I}„\ddot{I}„$ signals are included in addition. In this article, we perform a feasibility study for discovering such a new scalar $S$ at future electron-positron colliders using the recoil-mass method applied to $e^{+}{e}^{-}\to ZS$ with $Z\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ and $S\to b\bar{b}$. For this, we employ a Deep Neural Network to enhance the separation between the Standard Model background and the signal, reducing the required integrated luminosity necessary for discovery by a factor of two to three. As a result, an $SU(2{)}_L$ singlet Higgs with a mass of $\approx$\,95\,GeV can be observed with more than 5$\ddot{I}ƒ$ significance at a 250\,GeV centre-of-mass energy collider with $5{\mathrm{ab}}^{-1}$ integrated luminosity if it has a mixing angle of at least $0.1$ with the Standard Model Higgs, which means that a discovery can be achieved within the whole 95\% confidence-level region preferred by Large Electron Positron excess. Furthermore, including more decay channels such as $S\to \ddot{I}„\ddot{I}„$ and $Z\to e^{+}{e}^{-}$ further enhances the discovery potential of future $e^{+}{e}^{-}$ accelerators, like CEPC, CLIC, FCC-ee and ILC.

5 pages, 2 captioned figures, 1 Table. To be appear in Physics Letters B (2025)