The decays $\omega /\varphi \to 3\pi$ are considered in the dispersive framework that is based on the isobar decomposition and subenergy unitarity. The inelastic contributions are parametrized by the power series in a suitably chosen conformal variable that properly accounts for the analytic properties of the amplitude. The Dalitz plot distributions and integrated decay widths are presented. Our results indicate that the final-state interactions may be sizable. As a further application of the formalism we also compute the electromagnetic transition form factors of $\omega /\varphi \to {\pi }^0{\gamma }^{*}$.

A resonancelike structure, the $P_c(4450)$, has recently been observed in the $J/\psi p$ spectrum by the LHCb Collaboration. We discuss the feasibility of detecting this structure in $J/\psi$ photoproduction in the CLAS12 experiment at JLab. We present a first estimate of the upper limit for the branching ratio of the $P_c(4450)$ to $J/\psi p$. Our estimates, which take into account the experimental resolution effects, predict that it will be possible to observe a sizable cross section close to the $J/\psi$ production threshold and shed light on the $P_c(4450)$ resonance in the future photoproduction measurements.

The microscopic nature of the XYZ states remains an unsettled topic. We show how a thorough amplitude analysis of the data can help constraining models of these states. Specifically, we consider the case of the Z(c)(3900) peak and discuss possible scenarios of a QCD state, virtual state, or a kinematical enhancement. We conclude that current data are not precise enough to distinguish between these hypotheses, however, the method we propose, when applied to the forthcoming high-statistics measurements should shed light on the nature of these exotic enhancements

We present a unitary dispersive model for the $\eta \to 3\pi$ decay process based upon the Khuri-Treiman equations which are solved by means of the Pasquier inversion method. The description of the hadronic final-state interactions for the $\eta \to 3\pi$ decay is essential to reproduce the available data and to understand the existing discrepancies between Dalitz plot parameters from experiment and chiral perturbation theory. Our approach incorporates substraction constants that are fixed by fitting the recent high-statistics WASA-at-COSY data for $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$. Based on the parameters obtained, we predict the slope parameter for the neutral channel to be $\alpha =-0.022\pm 0.004$. Through matching to next-to-leading-order chiral perturbation theory, we estimate the quark mass double ratio to be $Q=21.4\pm 0.4$.

We report measurements of the photon beam asymmetry $\mathrm{\Sigma }$ for the reactions $\vec{\gamma }p\to p{\pi }^0$ and $\vec{\gamma }p\to p\eta$ from the GlueX experiment using a 9 GeV linearly polarized, tagged photon beam incident on a liquid hydrogen target in Jefferson Lab's Hall D. The asymmetries, measured as a function of the proton momentum transfer, possess greater precision than previous ${\pi }^0$ measurements and are the first $\eta$ measurements in this energy regime. The results are compared with theoretical predictions based on $t$-channel, quasiparticle exchange and constrain the axial-vector component of the neutral meson production mechanism in these models.