0000000000553860
AUTHOR
D. Werthmueller
Measurement of the decay η′→π0π0η at MAMI
An experimental study of the eta' -> pi(0)pi(0)eta -> 6 gamma decay has been conducted with the best up-to-date statistical accuracy, by measuring. 0 mesons produced in the gamma p -> eta'p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the eta' -> pi(0)pi(0)eta matrix element are consistent with the most recent results for eta' -> pi pi eta decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the pi(+)pi(-) thorn p-mass threshold, the magnitude and sign of which, checked within the framewo…
Accurate Test of Chiral Dynamics in the \boldmath$\vec{\gamma} p \rightarrow \pi^0p$ Reaction
A precision measurement of the differential cross sections $d\sigma/d\Omega$ and the linearly polarized photon asymmetry $\Sigma \equiv (d\sigma_\perp - d\sigma_\parallel) \slash (d\sigma_\perp + d\sigma_\parallel)$ for the $\vec{\gamma} p \rightarrow \pi^0p$ reaction in the near-threshold region has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multi-photon detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$- and all three $P$-wave amplitudes for the first t…
Photoproduction of $\eta$ $\pi$ pairs off nucleons and deuterons
Quasi-free photoproduction of $\pi\eta$-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi\eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of $…
Study of $\eta$ and $\eta'$ photoproduction at MAMI
The reactions $\gamma p\to \eta p$ and $\gamma p\to \eta' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation functions for $\eta$ photoproduction at the energies in vicinity of the $\eta'$ threshold, $W=1896$MeV ($E_\gamma=1447$MeV). This behavior is explained in a revised $\eta$MAID isobar model by a significant branching of the $N(1895)1/2^-$ nucleon resonance to both, $\eta p$ and $\eta'…