The REDTOP experiment: Rare $η/η^{\prime}$ 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.

Axion-meson mixing in light of recent lattice $η$-$η'$ simulations and their two-photon couplings within $U(3)$ chiral theory

“…[9,10]. Recently many works aiming at the extended descriptions of the axion-η ( ′ ) interactions are proposed from different points of view [11][12][13][14][15][16][17][18][19][20], including the axion production from the η/η ′ and kaon decays, CP violating axion signals, the axion-baryon couplings, the model-independent part of the axion-photon-photon coupling, etc. In this work, we will further pursue a systematical calculation of the axion-φ (φ = π, η, η ′ ) interactions order by order within the U (3) χPT by employing the δ expansion scheme [21][22][23], namely, a simultaneous expansion in powers of the momenta, light-quark masses and 1/N C , i.e.…”

Semileptonic decays of $ρ$, $ω$, $ϕ$, $η$ and $η'$ mesons in ground and first radially excited states in the $U(3)\times U(3)$ NJL model

“…It is important to note that a program is being developed for a new experimental η meson factory REDTOP [30,31], where mesons will be generated by a proton beam at Fermilab or at the proton synchrotron at CERN. It is expected that the number of events at the new factory will be 2 orders of magnitude greater than previous experiments.…”

Sensitivity of the $η^{(\prime)}\toπ^{0}γγ$ and $η^{\prime}\toηγγ$ decays to a sub-GeV leptophobic $U(1)_{B}$ boson

“…An increasingly ubiquitous strategy to search for physical phenomena beyond the Standard Model (BSM) is to test fundamental symmetries, such as C, P, T , CP, and CPT , in different processes. Specifically, decays of the neutral pseudoscalar mesons η and η constitute a particularly suited playground to look for new physics [1,2]. This is because these two mesons are special, as they are eigenstate of the C, P, CP and G-parity operators, and all their strong and electromagnetic decays are either anomalous or forbidden at lowest order due to the conservation of fundamental symmetries of QCD.…”

“…This is because these two mesons are special, as they are eigenstate of the C, P, CP and G-parity operators, and all their strong and electromagnetic decays are either anomalous or forbidden at lowest order due to the conservation of fundamental symmetries of QCD. Consequently, higher order contributions are expected to become relevant, rendering the η/η decays sensitive hadronic probes to test fundamental symmetries and to search for undiscovered fundamental BSM particles, such as dark photons or leptophobic U(1) B bosons (see [1,2] and references therein). An example are the rare η ( ) → π 0 γγ and η → ηγγ which, as they are highly suppressed in the Standard Model (SM) [3][4][5][6][7], have been put forward as fine probes to search for MeV-GeV signatures of a new leptophobic B boson [8] arising from a new U(1) B gauge symmetry which couples predominantly to quarks over leptons [9][10][11][12][13].…”

“…The Belle collaboration has also pursued searches for a B boson decaying into π + π − using η → π + π − γ decays [38] but have found no signal and, since B → π + π − is suppressed by G-parity conservation, the limits on the Bboson parameters are not as stringent as the constraints coming from other decays, such as the η → π 0 γγ. B-boson searches may also be carried out at future η/η factories, such as the proposed REDTOP experiment [2], 1 or in direct photoproduction γ p → Bp → π + π − π 0 p at the GlueX experiment at Jefferson Lab [39], which will probe B-boson masses above 0.5 GeV. Alternatively, signals of U(1) B bosons decaying into invisible particles, i.e.…”