The decay $\rho^{0}\to \pi^{0}\pi^{0}\gamma$ and the role of $\sigma$-meson

We present theoretical results for $(\gamma, \pi^0 \pi^0)$ production on nucleons and nuclei in the kinematical region where the scalar isoscalar $\pi \pi$ amplitude is influenced by the $\sigma$ pole. The final state interaction of the pions modified by the nuclear medium produces a spectacular shift of strength of the two pion invariant mass distribution induced by the moving of the $\sigma$ pole to lower masses and widths as the nuclear density increases.

We briefly summarize current experimental and theoretical results on the $\pi^0$ Dalitz decay, including the new value for the ratio $R={\Gamma(\pi^0\to e^+e^-\gamma(\gamma))}/{\Gamma(\pi^0\to\gamma\gamma)}=11.978(6)\times10^{-3}$, which is by two orders of magnitude more precise than the current PDG average. Furthermore, we discuss radiative corrections for the Dalitz decays $\eta^{(\prime)}\to\ell^+\ell^-\gamma$ beyond the soft-photon approximation. The corrections inevitab...

We present theoretical results for (gamma,pi0 pi0) and (gamma,pi+- pi0) production on nucleons and nuclei in the kinematical region where the scalar isoscalar pi pi amplitude is influenced by the sigma pole. The final state interaction of the pions modified by the nuclear medium produces a spectacular shift of strength of the pi0 pi0 invariant mass distribution induced by the moving of the sigma pole to lower masses and widths as the nuclear density increases.

Cross sections for the $\pi^+\pi^-$ events arising due to the decay of $\rho^0$ meson have been calculated. This rho meson is considered to produce coherently in the $(p,p^\prime)$ reaction on a nucleus. The distorted wave functions for the continuum particles and the rho meson propagator are described by the eikonal form. The sensitivity of the cross section on the pion emission angle as well as on the beam energy has been investigated. The cross sections for the $\rho^0$ de...

In view of the recent interest in the decays of mesons into a pair of light leptons, a computation of the QED radiative corrections to the decay of $\pi^{0}$ into an electron-positron pair is presented here. The results indicate that the peak value of the differential decay rate is reduced by about $50 \%$, because of soft-photon radiation. The number of $e^{+}e^{-}$ pairs having invariant masses in an energy bin of 0.5 MeV centered around $m_{\pi}$ is found to be about $20 \...

We study the radiative decay $\phi\to\pi^{0}\eta\gamma$ within the framework of a phenomenological approach in which the contributions of $\rho$-meson, chiral loop and $a_0$-meson are considered. We analyze the interference effects between different contributions and utilizing the experimental branching ratio and invariant $\pi^0\eta$ mass spectrum for $\phi\to\pi^{0}\eta\gamma$ decay we estimate the branching ratio of $\phi\to a_0\gamma$ decay.

The study of the $\pi N\to \rho^0 N$ and $\pi N \to \omega N$ amplitudes below and close to the vector meson production threshold ($1.4<\sqrt s <1.8$ GeV)reveals a rich structure arising from the presence of baryon resonances in this energy range. These resonances are reflected in the interference pattern of the $e^+e^-$ decays of the $\rho^0$- and $\omega$-mesons produced in $\pi^- p$ and $\pi^+ n$ reactions. We discuss the shape and magnitude of the $\rho^0$-$\omega$ interf...

The problem of $\rho$- and $\omega$- mesons contributions to the background for $\eta \to \pi^0 e^+e^-$ decay and to the asymmetries in the decays $\eta \to \pi^+\pi^-\pi^0$ and $\eta \to \pi^+\pi^-\gamma$ is considered.

The $\rho_2$ meson is the missing isovector member of the meson nonet with the quantum numbers $J^{PC}=2^{--}$. It belongs to the class of $\rho$-mesons such as the vector meson $\rho(770)$, the excited vector $\rho(1700)$ and the tensor $\rho_3(1690)$. Yet, despite the rich experimental and theoretical studies for other $\rho$-meson states, no resonance that could be assigned to the $\rho_2$ meson has been measured. In this note, we present the results for the mass and domin...

We reexamine the $\omega \to \pi^{0} \pi^{0} \gamma $ decay, adding the effect of $\omega-\rho$ mixing to the amplitude calculated with the aid of chiral perturbation theory and vector meson dominance. We predict the neutral decay to occur with a width of $\Gamma($\omega \to \pi^{0} \pi^{0} \gamma $) =(390\pm96) {\rm eV}$ and also analyze the effect of the $\omega-\rho$ mixing on the $\Gamma($\omega \to \pi^{0} \pi^{0} \gamma $)/ \Gamma($\omega \to \pi^{+} \pi^{-} \gamma $)$ ...