Eta meson

Abstract: Since the discovery of the first charmed meson in 1976, many open-charm and open-bottom hadrons were observed. In 2003 two narrow charm-strange states $D_{s0}^*(2317)$ and $D_{s1}(2460)$ were discovered by the BaBar and CLEO Collaborations, respectively. After that, more excited heavy hadrons were reported. In this work, we review the experimental and theoretical progress in this field.

Abstract: We determine masses and decay constants of heavy-heavy and heavy-charm pseudoscalar mesons as a function of heavy quark mass using a fully relativistic formalism known as highly improved staggered quarks for the heavy quark. We are able to cover the region from the charm quark mass to the bottom quark mass using MILC ensembles with lattice spacing values from 0.15 fm down to 0.044 fm. We obtain ${f}_{{B}_{c}}=0.427(6)\text{ }\text{ }\mathrm{GeV}$; ${m}_{{B}_{c}}=6.285(10)\text{ }\text{ }\mathrm{GeV}$ and ${f}_{{\ensuremath{\eta}}_{b}}=0.667(6)\text{ }\text{ }\mathrm{GeV}$. Our value for ${f}_{{\ensuremath{\eta}}_{b}}$ is within a few percent of ${f}_{\ensuremath{\Upsilon}}$, confirming that spin effects are surprisingly small for heavyonium decay constants. Our value for ${f}_{{B}_{c}}$ is significantly lower than potential model values being used to estimate production rates at the LHC. We discuss the changing physical heavy-quark mass dependence of decay constants from heavy-heavy through heavy-charm to heavy-strange mesons. A comparison between the three different systems confirms that the ${B}_{c}$ system behaves in some ways more like a heavy-light system than a heavy-heavy one. Finally we summarize current results on decay constants of gold-plated mesons.

Abstract: We identify the leading s-wave amplitudes of the SU(3) chiral meson-baryon Lagrangian with an effective coupled-channel potential which is iterated in a Lippmann-Schwinger equation. The strangeness $S=-1$ resonance $\Lambda(1405)$ and the $S_{11}(1535)$ nucleon resonance emerge as quasi-bound states of anti-kaon/nucleon and kaon/$\Sigma$-hyperon. Our approach to meson photoproduction introduces no new parameters. By adjusting a few finite range parameters we are able to simultaneously describe a large amount of low energy data. These include the cross sections of $K^-p$ elastic and inelastic scattering, the cross sections of eta meson and kaon photoproduction from nucleons as well as those of pion induced production of etas and kaons (16 different reaction channels altogether).