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Register a new userOmega and Eta (Eta-prime) mesons from NN and ND collisions at intermediate energies
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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.
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The hadronic decays eta, eta-prime -> 3 pi and eta-prime -> eta pi pi are investigated within the framework of U(3) chiral effective field theory in combination with a relativistic coupled-channels approach. Final state interactions are included by deriving s- and p-wave interaction kernels for meson-meson scattering from the chiral effective Lagrangian and iterating them in a Bethe-Salpeter equation. Very good overall agreement with currently available data on decay widths and spectral shapes is achieved.
Various decays of eta and eta-prime are investigated within the framework of U(3) chiral effective field theory in combination with a relativistic coupled-channels approach. Final state interactions are included by deriving s- and p-wave interaction kernels for meson-meson scattering from the chiral effective Lagrangian and iterating them in a Bethe-Salpeter equation. Very good agreement with experimental data is achieved.
We determine the masses, the singlet and octet decay constants as well as the anomalous matrix elements of the $eta$ and $eta^prime$ mesons in $N_f=2+1$ QCD@. The results are obtained using twenty-one CLS ensembles of non-perturbatively improved Wilson fermions that span four lattice spacings ranging from $aapprox 0.086,$fm down to $aapprox 0.050,$fm. The pion masses vary from $M_{pi}=420,$MeV to $126,$MeV and the spatial lattice extents $L_s$ are such that $L_sM_pigtrsim 4$, avoiding significant finite volume effects. The quark mass dependence of the data is tightly constrained by employing two trajectories in the quark mass plane, enabling a thorough investigation of U($3$) large-$N_c$ chiral perturbation theory (ChPT). The continuum limit extrapolated data turn out to be reasonably well described by the next-to-leading order ChPT parametrization and the respective low energy constants are determined. The data are shown to be consistent with the singlet axial Ward identity and, for the first time, also the matrix elements with the topological charge density are computed. We also derive the corresponding next-to-leading order large-$N_{c}$ ChPT formulae. We find $F^8 = 115.0(2.8)~text{MeV}$, $theta_{8} = -25.8(2.3)^{circ}$, $theta_0 = -8.1(1.8)^{circ}$ and, in the $overline{mathrm{MS}}$ scheme for $N_f=3$, $F^{0}(mu = 2,mathrm{GeV}) = 100.1(3.0)~text{MeV}$, where the decay constants read $F^8_eta=F^8cos theta_8$, $F^8_{eta^prime}=F^8sin theta_8$, $F^0_eta=-F^0sin theta_0$ and $F^0_{eta^prime}=F^0cos theta_0$. For the gluonic matrix elements, we obtain $a_{eta}(mu = 2,mathrm{GeV}) = 0.0170(10),mathrm{GeV}^{3}$ and $a_{eta^{prime}}(mu = 2,mathrm{GeV}) = 0.0381(84),mathrm{GeV}^{3}$, where statistical and all systematic errors are added in quadrature.
The PHENIX experiment at the Relativistic Heavy Ion Collider measured $pi^0$ and $eta$ mesons at midrapidity in U$+$U collisions at $sqrt{s_{_{NN}}}=192$ GeV in a wide transverse momentum range. Measurements were performed in the $pi^0(eta)rightarrowgammagamma$ decay modes. A strong suppression of $pi^0$ and $eta$ meson production at high transverse momentum was observed in central U$+$U collisions relative to binary scaled $p$$+$$p$ results. Yields of $pi^0$ and $eta$ mesons measured in U$+$U collisions show similar suppression pattern to the ones measured in Au$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV for similar numbers of participant nucleons. The $eta$/$pi^0$ ratios do not show dependence on centrality or transverse momentum, and are consistent with previously measured values in hadron-hadron, hadron-nucleus, nucleus-nucleus, and $e^+e^-$ collisions.
We consider the chiral Lagrangian with a nonet of Goldstone bosons and a nonet of light vector mesons. The mixing between the pseudoscalar mesons eta and eta-prime is taken into account. A novel counting scheme is suggested that is based on hadrogenesis, which conjectures a mass gap in the meson spectrum of QCD in the limit of a large number of colors. Such a mass gap would justify to consider the vector mesons and the eta-prime meson as light degrees of freedom. The complete leading order Lagrangian is constructed and discussed. As a first application it is tested against electromagnetic transitions of light vector mesons to pseudoscalar mesons. Our parameters are determined by the experimental data on photon decays of the omega, phi and eta-prime meson. In terms of such parameters we predict the corresponding decays into virtual photons with either dielectrons or dimuons in the final state.
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