S = 0 Pseudoscalar Meson Photoproduction from the Proton

Many measurements of pseudoscalar mesons with S = 0 photoproduced on the proton have been made recently. These new data are particularly useful in theoretical investigations of nucleon resonances. How the new data from various labs complement each other and help fill in the gaps in the world data set is disscussed, with a glance at measurements to be made in the near future. Some theoretical techniques used to explain the data are briefly described. The S = 0 pseudoscalar mesons include the π 0 , π + , η, and η ′. The pions, as the lightest mesons, are copiously produced in the strong interaction. Pion photoproduction data have been vital to gain a first glimpse of the nucleon resonance spectrum. Whereas the pions have isospin 1, the η and η ′ mesons have isospin 0, so resonances decaying by emitting η or η ′ mesons can only have isospin 1 2. Thus, η and η ′ mesons act as " isospin filters " for the nucleon resonance spectrum. Further, as the only isosinglet, η ′ can be used to indirectly probe gluonic coupling to the proton through the flavor-singlet Goldberger-Treiman relation