The REDTOP experiment: a $η/η^{\prime}$ factory to explore dark matter and physics beyond the Standard Model
Marcin Zielinski, Corrado Gatto
TL;DR
REDTOP proposes a fixed-target, high-luminosity η/η' factory to search for BSM physics in the MeV–GeV range via rare decays. It organizes the search around four hidden-sector portals—vector, scalar, pseudoscalar, and heavy neutral leptons—exploiting the clean, flavor-conserving decays of η and η' with suppressed SM backgrounds. The detector concept emphasizes near 4π acceptance, fast timing, and high-efficiency lepton/photon identification to operate at rates near $1$ GHz, achieving yields of >$10^{13}$ η and >$10^{12}$ η' per year. If successful, REDTOP could reach branching ratios as low as $10^{-12}$ and provide crucial tests of QCD axions/ALPs, HNLs, CP violation, and lepton-flavor phenomena, complementing high-energy collider searches.
Abstract
The REDTOP experiment is a proposed super-$η$/$η'$ factory aimed at exploring physics beyond the Standard Model in the MeV-GeV range and rare $η$/$η'$ meson decays. With projected production rates exceeding $10^{13}$ $η$/year and $10^{12}$ $η'$/year, REDTOP will enable studies of symmetry violations and all four portals to the Dark Sector. Preliminary studies show sensitivity, which could open a broad possibility for exploring new physics and contribute to a deeper understanding of fundamental interactions within the Standard Model. Such high statistics experiments and the required sensitivity can only be achieved with a high intensity proton or pion beam, available at several accelerator facilities worldwide. This article discusses the physics potential of the REDTOP experiment, the detector design, and the future beam requirements.