Project A: Study of light mesons in two-photon interaction

Project leader: PD Dr. Fritz-Herbert Heinsius, Ruhr-Universität Bochum

The goal of this project is to study the production of light mesons in two-photon interaction at the BESIII experiment. Here specifically the f0,f2,a0,a22and η2 mesons can be produced. The analysis should provide data on the two-photon width of the different states. This gives clue to the nature of the resonances itself by measuring their behavior in this electromagnetic process. Therefore the project will concentrate on the most promising decay channels, where from previous experiments only limited experimental data on the two-photon interaction is available. Different decay channels are studied to disentangle overlapping resonances. During the first three years period the project concentrated on the decay channels K+K, ηπ+π, ηπ0 and 3π0. Within the next three year period we will add the channels π0η, ηη, π+ππ0 and KS0KS0 to perform a coupled channel analysis and add more complicated channels like KKπ.

This Teilprojekt will help to solve long existing puzzles of the past concerning suspected glueball signals due to the quality of the data: How strongly is the f0(1710) produced in γγ collisions? Is the f0(1500) produced in γγ collisions at all? How can the puzzle of η(1295), η(1405) and η be interpreted?

The data will be analyzed together with the results of the measurements of the research group of U. Wiedner in a coupled channel analysis. Further comparisons will be done with the KK and KK* decays in the “Open Charm Decays of Exotics” project of M. Fritsch. To reveal the nature of the different states the different production mechanisms are compared. The search for tetra quarks in the light quark sector will be compared to the tetra quark results in the project “Hidden charm exotics at BES” (K. Peters) and “Search for exotics in baryon-antibaryon states” (A. Khoukaz) and should provide valuable input to the models.