Decays Of Light Pseudoscalar Mesons Research Articles

Note on invisible decays of light mesons

A search for the invisible decays of $\omega$ and $\phi$ mesons in $J/\psi\to \omega (\phi)\eta$ transitions has been performed by the BESIII Collaboration very recently. Inspired by this experimental study, we compute the lowest order contribution to branching ratios of ${\cal B}(V\to\bar{\nu}\nu)$ with $V$ denoting $\rho,\;\omega,\;\phi$, as the standard model background to these invisible decays. Our predictions are far below the upper bounds given by the BESIII experiment. We also analyze the $J/\psi\to \eta(\eta^\prime)\bar{\nu}\nu$ processes, and estimate their decay rates. Furthermore, the invisible decays of light pseudoscalar mesons $P$ including $\pi^0$, $\eta$, and $\eta^\prime$ are reexamined in the present note. It is shown that, due to the helicity suppression of the two-neutrino final state, the standard model contributions to $P\to{\rm invisible}$ decays are dominated by $P\to\bar{\nu}\nu \bar{\nu}\nu$ processes.

Pseudoscalar meson transition form factors in nonperturbative QCD approach

In this communication we discuss a few topics related to modern experimental data on physics of light pseudoscalar mesons. It includes the contribution of the pseudoscalar mesons to the muon anomalous magnetic moment (AMM), g − 2 , rare decays of light pseudoscalar mesons to a lepton pair, transition form factors of pseudoscalar mesons at large momentum transfer, the pion transversity form factor. Measuring the muon anomalous magnetic moment g − 2 and rare decays of light pseudoscalar mesons into a lepton pair P → l + l − serve as important test of the standard model. To reduce the theoretical uncertainty in the standard model predictions, the data on the transition form factors of light pseudoscalar mesons play significant role. Recently new data on behavior of these form factors at large momentum transfer was supplied by the BABAR collaboration. Within the nonlocal chiral quark model it is shown how to describe these data and how the meson distribution amplitude evolves as a function of the dynamical quark masses and meson masses.

Light meson physics with Crystal Ball/MAMI and at BES-III

Rare decays of light mesons like η, η′, and ω offer excellent possibilities to study fundamental symmetries and symmetry-breaking patterns. Furthermore, electromagentic transitions with vertices Pγ*γ as in decays of light pseudoscalar mesons (P) or meson production in e+e− collisions give insight into hadronic structure through transition form factors and produce additional constraints for the determination of the anomalous magnetic moment of the muon (g − 2)μ. In this article, recent results on η and ω decays from the Crystal Ball at MAMI experiment as well as feasibility studies on transition form factors for the Crystal Ball and the BES–III at BEPC–II facility are presented.

Pion form factors and decays

In this communication we discuss few topics related with modern experimental data on the physics of light pseudoscalar mesons. It includes the contribution of the pseudoscalar mesons to the muon anomalous magnetic moment (AMM), the rare decays of light pseudoscalar mesons to lepton pair, g –2, the transition form factors of pseudoscalar mesons at large momentum transfer, the pion transversity form factor. Measuring the muon anomalous magnetic moment g –2 and the rare decays of light pseudoscalar mesons into lepton pair P → l + l − serve as important test of the standard model. To reduce the theoretical uncertainty in the standard model predictions the data on the transition form factors of light pseudoscalar mesons play significant role. Recently new data on behavior of these form factors at large momentum transfer was supplied by the BABAR collaboration.

How the recent BABAR data for P → γγ* affect the Standard Model predictions for the rare decays P → l + l −

Measuring the lepton anomalous magnetic moments (g − 2) and the rare decays of light pseudoscalar mesons into lepton pairs P → l + l −, serve as important tests of the Standard Model. To reduce the theoretical uncertainty in the standard model predictions, the data on the charge and transition form factors of the light pseudoscalar mesons play a significant role. Recently, new data on the behavior of the transition form factors P → γγ* at large momentum transfer were supplied by the BABAR collaboration. There are several problems with the theoretical interpretation of these data: (1) An unexpectedly slow decrease of the pion transition form factor at high momenta, (2) the qualitative difference in the behavior of the pion form factor and the η and η′ form factors at high momenta, (3) the inconsistency of the measured ratio of the η and η′ form factors with the predicted one. We comment on the influence of the new BABAR data on the rare decay branchings.

Transition form factors [formula omitted], rare decays [formula omitted] and muon g–2

Measuring the muon anomalous magnetic moment g − 2 and the rare decays of light pseudoscalar mesons into a lepton pair P → l + l − serve as important tests of the standard model. To reduce the theoretical uncertainty in the standard model predictions, the data on the transition form factors of light pseudoscalar mesons play a significant role. Recently, new data on the behavior of these form factors at large momentum transfer were supplied by the BABAR collaboration. We comment on the (in)consistency of these data with perturbative QCD expectations and their influence on the rare decays.

Muon [formula omitted], rare decays [formula omitted] and transition form factors [formula omitted

Measuring the muon anomalous magnetic moment g-2 and the rare decays of light pseudoscalar mesons into lepton pair P \to l+l- serve as important test of the standard model. To reduce the theoretical uncertainty in the standard model predictions the data on the transition form factors of light pseudoscalar mesons play significant role. Recently new data on behavior of these form factors at large momentum transfer was supplied by the BABAR collaboration. We comment on the (in)consistency of these data with perturbative QCD expectation.

Lepton-flavor violation in light hadron decays

The lepton-flavor-violating decays of light pseudoscalar mesons and light baryons are investigated within extensions of the $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}U(1)$ model. These models contain heavy Dirac or Majorana neutrinos and allow large lepton--heavy-neutrino mixings. The free-parameter space of these models is carefully studied. Special care is devoted to the comparison of results of different models. A large ``nondecoupling'' window is found, and the decoupling of extremely heavy neutrinos is explicitly shown in all models except one, for which the free-parameter space is bounded. Among the decays studied, the experimentally most interesting decays are ${K}_{L}\ensuremath{\rightarrow}e\ensuremath{\mu}$ and ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}e\ensuremath{\mu}$. The ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}e\ensuremath{\mu}$ decay is found to be equally interesting for the study of lepton-flavor violation as ${K}_{L}\ensuremath{\rightarrow}e\ensuremath{\mu}$ decay. The constraint on the model parameters, coming from the nonobservation of the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e\ensuremath{\gamma}$ decay, leads to the maximal decay rates ${B(K}_{L}\ensuremath{\rightarrow}e\ensuremath{\mu})\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ and $B({\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}e\ensuremath{\mu})\ensuremath{\lesssim}{(2n}_{R}\ensuremath{-}2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$, where ${n}_{R}$ is number of heavy neutrinos, much smaller than the present experimental upper limits.