Measurement of differential cross sections for processesγd→pn, π0d, and pXin the energy range of dibaryon resonances

Abstract

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.