Session JJ: Mini-Symposium: Light Meson Decays I

Precision tests of fundamental physics with π0, η and η′ mesons

Decays of π^0, η and η′ mesons provide a unique laboratory to test low-energy Quantum Chromodynamics and search for new physics beyond the Standard Model. They have drawn world-wide attention in recent years and have inspired broad experimental programs in different high-intensity-frontier centers. In this talk we will highligh some of the most important opportunities provided by these decays emphasizing those that allow for simultaneous precision Standard Model tests and searches for beyond the Standard Model physics, looking either for discrete symmetry violation or potential new light particles.   

η-Meson Decays with GlueX

The GlueX experiment primarily conducts searches for hybrid mesons, using a linearly polarized photon beam, impinging on a liquid hydrogen target. The GlueX detector provides a close to 4π acceptance and allows to reconstruct both neutral and charged particle tracks which are produced in the γp reactions. This makes it an ideal system to measure and study η-Meson decays.

GlueX is running in two phases and the data collected so far corresponds to ∼826pb^-1 . The results from the first phase of GlueX will be reported in this presentation while the second phase has started in 2020 and is running at higher luminosities, using a DIRC upgrade for K/π separation. Additionally, the GlueX forward calorimeter will be updated which helps to improve the measurement of the rare η decay modes.

This talk will give a brief overview of the GlueX η-meson decay physics program, highlighting the latest results obtained from the ongoing data analysis. These include cross section measurements, study of symmetry breaking phenomena as well as the search for physics beyond the standard model.   

Model-independent description of C- and CP-violation in η decays

We present a model-independent, non-perturbative construction of the hadronic amplitudes η→π⁺π^– π⁰ and η'→ηπ⁺π^–, allowing for C- and CP-violating asymmetries in the π⁺π^– distributions. These amplitudes are consistent with the constraints of analyticity and unitarity. Our dispersive representation allows us to extract the individual coupling strengths of the C- and CP-violating contributions arising from effective isoscalar and isotensor operators in η→π⁺π^– π⁰ and an effective isovector operator in η'→ηπ⁺π^–. We furthermore discuss the possibility of deriving C- and CP-odd η decays in a model-independent manner from effective field theories.   

Dalitz plot analysis for the η'→ηππ decay with GlueX data

The dominant hadronic decay modes of the η', η'→ηπ⁺π^- and η'→ηπ⁰π⁰, are interesting for many reasons. First, the contribution of scalar resonances predominates, allowing for the study of the properties of the resonance f₀(500). Second, these decays allow us to perform tests of chiral perturbation theory and its possible extensions. Lastly, they offer the opportunity to constrain ηπ scattering.

In this talk, we report on the status of the Dalitz plot analysis for photoproduced η' in the reaction γp→pη', for the decay channel η'→ηππ using the Phase I data set recorded by the GlueX experiment in Hall D at Jefferson Laboratory.   

The Jefferson Lab Eta Factory.

The Jefferson Lab Eta Factory (JEF) aims to collect $5\times10^7~\eta^{(')}$, with the GlueX setup and an upgraded Forward Calorimeter, using an incident photon beam of $8-12$~GeV on a liquid hydrogen

  target. This large data set will enable the study of symmetry violation in hadron decay dynamics, and the search for new physics. Among the key decay channels is the decay

  $\eta \rightarrow \gamma\gamma\pi^0$ decay, which is sensitive to higher order terms of chiral perturbation theory, and can be used as a probe of low-energy QCD.

  The $\eta^{(')}\rightarrow 3\gamma$ decay, which is C violating, can be used to constrain further C-violating and P-conserving new physics. Additionally, $\eta^{(')}$ decays will offer sensitive probes

  for new hypothetical GeV scale dark particles (dark photons-like, dark Higgs bosons-like, and axion-like particles). In this talk, I will present the physics objectives and status of the JEF

  experimental program.

    

The REDTOP experiment: a $\eta$/$\eta'$ factory to explore dark matter and physics beyond the Standard Model

The $\eta$ and $\eta'$ mesons are almost unique in the particle universe since they are Goldstone boson and the dynamics of their decay are strongly constrained.  The integrated eta meson samples collected in earlier experiments have been about ~$10^9$ events, dominated by the WASA at Cosy experiment, limiting considerably the search for such rare decays.  A new experiment, REDTOP, is being proposed, aiming at collecting more than $10^{14}$ eta/yr ($10^{12}$ eta'/yr) for studying of rare $\eta$ decays. 

Such statistics are sufficient for investigating several symmetry violations, and for searches of new particles beyond the Standard Model.

Recent physics and detector studies indicate that REDTOP has excellent sensitivity to probe all four portals connecting the dark sector with the Standard Model. Furthermore, conservation laws and violation of discrete symmetries can be probed in several ways. 

The physics program and the detector for REDTOP will be discussed during the presentation.