Eur. Phys. J. C (2025) 85: 1404
https://doi.org/10.1140/epjc/s10052-025-15094-w

Regular Article - Theoretical Physics

Search for sub-GeV scalars in $e^{+}{e}^{-}$ collisions

¹ Departamento de Física, Universidade Federal de Campina Grande, Campina Grande, PB, Brazil
² Millennium Institute for Subatomic Physics at High-Energy Frontier (SAPHIR), Fernandez Concha 700, Santiago, Chile
³ International Institute of Physics, Universidade Federal do Rio Grande do Norte, Campus Universitário, Lagoa Nova, 59078-970, Natal, RN, Brazil
⁴ Center for Theoretical and Experimental Particle Physics-CTEPP, Facultad de Ciencias Exactas, Universidad Andres Bello, Fernandez Concha 700, Santiago, Chile
⁵ Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, 59078-970, Natal, Rio Grande do Norte, Brazil
⁶ Departamento de Fisica, Facultad de Ciencias, Universidad de La Serena, Avenida Cisternas 1200, La Serena, Chile
⁷ Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-580, Santo André, SP, Brazil
⁸ Laboratoire de Physique Theorique et Hautes Energies (LPTHE), UMR 7589, Sorbonne Universite et CNRS, 4 place Jussieu, 75252, Paris Cedex 05, France

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Received: 27 August 2025
Accepted: 20 November 2025
Published online: 10 December 2025

Abstract

Light scalars that couple to leptons are common figures in beyond the Standard Model endeavors. Considering a scalar that has universal and couplings to leptons only, we compute this leptophilic scalar contribution to the $e^{-}{e}^{+}\to {\tau }^{+}{\tau }^{-}S$ production cross section with $S\to e^{+}{e}^{-}({\mu }^{+}{\mu }^{-})$. We later compare the expected signal with recent data from the BELLE collaboration collected near the resonance $\mathrm{{\rm Y}}(4S)$ with $\mathcal{L}=626f{b}^{-1}$ of integrated luminosity to place limits on the couplings-mass plane for the 4 MeV-6.5 GeV mass range. We then extended this analysis to a more general one $e^{-}{e}^{+}\to {\ell }^{+}{\ell }^{-}S$ production cross section where $\ell =e,\mu ,\tau$ with $S\to e^{+}{e}^{-}({\mu }^{+}{\mu }^{-})$, showing that BELLE constitutes an excellent laboratory for light scalars, where can be derived constraints stronger than those derived stemming from the g-2 of the electron or muon.