The REDTOP experiment: Rare $\eta/\eta^{\prime}$ Decays To Probe New Physics

Abstract

The η and η mesons are nearly unique in the particle universe since they are almost Goldstone bosons and the dynamics of their decays are strongly constrained. The integrated η-meson samples collected in earlier experiments amount to ∼ 10 9 events. A new experiment, REDTOP (Rare Eta Decays To Observe Physics Beyond the Standard Model), is being proposed, with the intent of collecting a data sample of order 10 14 η (10 12 η ) for studying very rare decays. Such statistics are sufficient for investigating several symmetry violations, and for searching for particles and fields beyond the Standard Model. In this work we present several studies evaluating REDTOP sensitivity to processes that couple the Standard Model to New Physics through all four of the so-called portals: the Vector, the Scalar, the Axion and the Heavy Lepton portal. The sensitivity of the experiment is also adequate for probing several conservation laws, in particular CP , T and Lepton Universality, and for the determination of the η form factors, which is crucial for the interpretation of the recent measurement of muon g − 2.

Improved limits on lepton-flavor-violating decays of light pseudoscalars via spin-dependent $μ\to e$ conversion in nuclei

“…[19] improves the previous limit [23] on the π 0 → µ − e + channel by an order of magnitude, leading to three independent constraints on π 0 → µe all at the level of 10 −10 [18 -20]. Limits on the analogous η, η decays are much weaker, but could be improved substantially at the planned JEF [24] and REDTOP [25] experiments.…”

Feebly-interacting particles: FIPs 2020 workshop report

“…The Rare η/η Decays To Probe New Physics experiment (REDTOP) is a fixedtarget meson factory [1266] searching for new physics in flavor-conserving rare decays of the η and η mesons. Such particles are almost unique in the particle universe, carrying the same quantum number as the Higgs boson except for parity, and no standard model (SM) charges, the dynamics of their decays is highly constrained.…”

Searching for a leptophobicBboson throughη→π0γγandηʹ→π0γγdecays

“…An increasingly ubiquitous strategy to search for new physics beyond the Standard Model (BSM) is to test fundamental symmetries in different processes. Decays of the pseudoscalar mesons η and η are particularly suited to achieve this goal [1,2]. Examples of this are the rare η ( ) → π 0 γγ decays which, as they are highly suppressed in the Standard Model (SM) [3], have been put forward as fine probes to search for sub-GeV signatures of a new leptophobic B boson [4] arising from a new U(1) B gauge symmetry which couples predominantly to quarks over leptons [5].…”

“…In fact, the search for leptophobic B bosons has been incorporated into the physics programmes of existing light-meson collaborations such as KLOE-II, which is searching for B bosons by looking for enhancements in the π 0 γ invariant mass spectrum of the φ → ηB → ηπ 0 γ process [6], and is a top priority physics goal for the recently approved Jefferson Lab Eta Factory (JEF) experiment, which promises a new and exciting era for η and η physics, with the η → π 0 γγ decay being their key signal channel. B-boson searches may also be carried out at future η/η facilities, such as the proposed REDTOP experiment [2].…”

“…It must be noted that the interaction Lagrangian in Eq. ( 1) is not completely decoupled from leptons as it contains subleading photon-like couplings to leptons proportional to ε = eg B /(4π) 2 .…”