Search

We report the final results of a search for narrow structures in the p-barp total cross section between 395 and 740 MeV/c with a rms mass resolution of 1.5 MeV around the S-resonance region. A reanalysis of the data significantly improved the statistical accuracy. No evidence is found for narrow structures and a 90%-confidence-level upper limit of 24 mb MeV is set at around 500 MeV/c for the integrated cross section of a Breit-Wigner-type resonance of width < or approx. =4 MeV.

The total p-barp cross section has been measured in the S region by the transmission method with use of beam-monitoring spectrometer. The result is inconsistent with the existence of the narrow resonance S(1936) with cross sections reported by previous experiments.

The differential cross section for the reactions $\ensuremath{\gamma}\mathrm{d}\ensuremath{\rightarrow}\mathrm{pn}$, $\ensuremath{\gamma}d\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\mathrm{d}$, and $\ensuremath{\gamma}\mathrm{d}\ensuremath{\rightarrow}\mathrm{p}X$ has been measured by using a tagged photon beam in the energy range of dibaryon resonances. The most characteristic feature of the data for $\ensuremath{\gamma}\mathrm{d}\ensuremath{\rightarrow}\mathrm{pn}$ is a forward nonpeaking angular distribution. This behavior is in complete disagreement with the existing predictions which take into account the dibaryon resonances. A phenomenological analysis is made by slightly modifying the model of the Tokyo group, but no satisfactory result is obtained. The data for $\ensuremath{\gamma}\mathrm{d}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\mathrm{d}$ at large angles show that the differential cross section decreases exponentially as a function of pion angle. A comparison is made with a Glauber model calculation. The result seems to be rather in favor of the existence of dibaryon resonances, but a clear conclusion is not possible because of a lack of more accurate data. In the process $\ensuremath{\gamma}\mathrm{d}\ensuremath{\rightarrow}\mathrm{p}X$, a broad peak due to quasifree pion production is observed, but the limitation of experimental sensitivity does not allow us to have a definite conclusion for the dibaryon resonance of mass 2.23 GeV conjectured by the Saclay group.

The differential cross section for $\ensuremath{\gamma}d\ensuremath{\rightarrow}\mathrm{pn}$ has been measured in the energy range between 180 and 600 MeV at c.m. angles 15\ifmmode^\circ\else\textdegree\fi{}, 30\ifmmode^\circ\else\textdegree\fi{}, 42\ifmmode^\circ\else\textdegree\fi{}, and 72\ifmmode^\circ\else\textdegree\fi{}, by using tagged photons. The results, in particular at smaller angles, are in disagreement with theoretical calculations which take into account the effect of dibaryon resonances.