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; A Zhevlakov

doi:10.1140/epjc/s10052-024-13421-1

Probing hidden leptonic scalar portals using the NA64 experiment at CERN

Eur Phys J C Part Fields. 2024;84(10):1035. doi: 10.1140/epjc/s10052-024-13421-1. Epub 2024 Oct 9.

Authors

A Ponten¹, H Sieber², B Banto Oberhauser², P Crivelli², D Kirpichnikov³, S N Gninenko^{3

4}, M Hösgen⁵, L Molina Bueno⁶, M Mongillo², A Zhevlakov^{7

8}

Affiliations

¹ Department of Physics and Astronomy, High Energy Physics, Uppsala University, Ångströmlaboratoriet, Lägerhyddsvägen 1, 752 37 Uppsala, Sweden.
² Institute for Particle Physics and Astrophysics, ETH Zürich, 8093 Zurich, Switzerland.
³ Institute for Nuclear Research of the Russian Academy of Sciences, 117312 Moscow, Russia.
⁴ Millennium Institute for Subatomic Physics at High-Energy Frontier (SAPHIR), Universidad Andres Bello, Fernandez Concha, 700 Santiago, Chile.
⁵ Helmholtz-Institut für Strahlen-und Kernphysik, Universität Bonn, 53115 Bonn, Germany.
⁶ Instituto de Fisica Corpuscular (CSIC/UV), Carrer del Catedratic Jose Beltran Martinez, 2, 46980 Paterna, Valencia Spain.
⁷ Bogoliubov Laboratory of Theoretical Physics, JINR, 141980 Dubna, Russia.
⁸ Matrosov Institute for System Dynamics and Control Theory SB RAS, Lermontov Str., 134, 664033 Irkutsk, Russia.

Abstract

In this study, we demonstrate the potential of the NA64 experiment at CERN SPS to search for New Physics processes involving $e \to μ$ transitions after the collision of 100 GeV electrons with target nuclei. A new Dark Sector leptonic portal in which a scalar boson $φ$ could be produced in the lepton-flavor-changing bremsstrahlung-like reaction, $e N \to μ N φ$ , is used as benchmark process. In this work, we develop a realistic Monte Carlo simulation of the NA64 experimental setup implementing the differential and total production cross-section computed at exact tree-level and applying the Weiszäcker-Williams phase space approximation. Using this framework, we investigate the main background sources and calculate the expected sensitivity of the experiment. The results indicate that with minor setup optimization, NA64 can probe a large fraction of the available parameter space compatible with the muon $g - 2$ anomaly and the Dark Matter relic predictions in the context of a new Dark Sector leptonic portal with $10^{11}$ EOT. This result paves the way to the exploration of lepton-flavour-changing transitions in NA64.