Probing hidden leptonic scalar portals using the NA64 experiment at CERN A. Ponten, H. Sieber, B. Banto Oberhauser, P. Crivelli, D. Kirpichnikov, S. N. Gninenko, M. Hösgen, L. Molina Bueno, M. Mongillo and A. Zhevlakov Eur. Phys. J. C, 84 10 (2024) 1035 Published online: 09 October 2024 DOI: 10.1140/epjc/s10052-024-13421-1