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Register a new userRare decays of eta-meson: the background of rho- and omega- mesons
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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.
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Isospin violating mixing of rho- and omega-mesons is reconsidered in terms of propagators. Its influence on various pairs of (rho^0,omega)-decays to the same final states is demonstrated. Some of them, (rho^0,omega)topi^+pi^- and (rho^0,omega)topi^0gamma, have been earlier discussed in the literature, others (e.g., (rho^0,omega)toetagamma and (rho^0,omega)to e^+e^-) are new in this context. Changes in partial widths for all the decay pairs are shown to be correlated. The set of present experimental data, though yet inconclusive, provides some limits for the direct (rhoomega)-coupling and indirectly supports enhancement of rho^0topi^0gamma in comparison with rho^{pm}topi^{pm}gamma, though not so large as in some previous estimates.
Influence of the isospin-violating (rho^0, omega)-mixing is discussed for any pair of decays of rho^0, omega into the same final state. It is demonstrated, in analogy to the CP-violation in neutral kaon decays, that isospin violation can manifest itself in various forms: direct violation in amplitudes and/or violation due to mixing. In addition to the known decays (rho^0, omega)topi^+pi^- and (rho^0, omega)topi^0gamma, the pair of decays to e^+e^- and the whole set of radiative decays with participation of rho^0, omega (in initial or final states) are shown to be also useful and perspective for studies. Existing data on these decays agree with the universal character of the mixing parameter and indirectly support enhancement of rho^0topi^0gamma in respect to rho^{pm}topi^{pm}gamma. Future precise measurements will allow to separate different forms of isospin violation and elucidate their mechanisms.
The investigation in the work of the reaction electron-positron to omega and pi0 mesons in the 3P0 nonrelativistic quark model reveals that the reaction electron-positron to omega and pi0 mesons process at the energy region from the omega and pi mesons threshold to 2.0 GeV is dominated by the two-step process in which the primary quark-antiquark pair first forms rho and rho mesons and then the vector mesons decay into omega and pi. With rho(1450) and rho(1700) mainly in 2S and 1D states respectively, the experimental data for the cross section of the reaction electron-positron to omega and pi0 mesons are well produced in the 3P0 quark model. The work supports the argument that rho(1450) is mainly a 2S meson and rho(1700) a 1D meson.
The production of pseudo scalar, Eeta, Eta-prime, and vector, Omega, Rho, Phi, mesons in NN collisions at threshold-near energies is analyzed within a covariant effective meson-nucleon theory. It is shown that a good description of cross sections and angular distributions, for vector meson production, can be accomplished by considering meson and nucleon currents only, while for pseudo scalar production an inclusion of nucleon resonances is needed. The di-electron production from subsequent Dalitz decay of the produced mesons, $etato gamma gamma^* togamma e^+e^-$ and $omegato pigamma^*to pi e^+e^-$ is also considered and numerical results are presented for intermediate energies and kinematics of possible experiments with HADES, CLAS and KEK-PS. We argue that the transition form factor $omegato gamma^*pi$ as well as $etato gamma^*gamma$ can be defined in a fairly model independent way and the feasibility of an experimental access to transition form factors is discussed.
We calculate diffractive photo- and leptoproduction of $rho$-, $rho$- and $rho$-mesons. The incoming photon dissociates into a $qbar{q}$-dipole which scatters on the nucleon and transforms into a vector meson state. The scattering amplitude is calculated in non-perturbative QCD with the model of the stochastic vacuum. Assuming that the physical $rho$- and $rho$-mesons are mixed states of an active 2S-excitation and some residual hybrid state which cannot be produced diffractively in lowest order QCD, we obtain good agreement with the data, especially the markedly different spectrum in the $pi^+pi^-$-invariant mass for photoproduction and $e^+e^-$-annihilation.
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