Multiple Meson Production by Photons in Hydrogen

Abstract

Pictures of a ${\mathrm{H}}_{2}$ diffusion cloud chamber with magnetic field taken at the 1.1-Bev Cornell synchrotron have been analyzed to study multiple meson production by photons on protons. They have yielded 108 cases of double charged meson production ($\ensuremath{\gamma}+p\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$) and 4 cases of triple meson production.For each event of double meson production, the energy of the incoming photon and the angles and momenta of the emitted particles could be determined. The most significant results are the following.The cross section for double charged meson production rises rapidly around 500 Mev to approximately 70 microbarns, a value of the same order as the total cross section for single meson production.In the reaction leading to a charged meson pair, ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ play dissimilar roles, as evidenced by the marked dissimilarities in their center-of-mass angular and momentum distributions. The $Q$-distributions suggest the interpretation that the predominant mode of pair production in the energy range from 500 to 700 Mev is ${N}^{*}+{\ensuremath{\pi}}^{\ensuremath{-}}$, ${N}^{*}\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{+}$, where ${N}^{*}$ likely is the resonant $\frac{3}{2}$, $\frac{3}{2}$ excited state of the proton. The fact that the angular distributions for the protons and the ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons are asymmetric about 90\ifmmode^\circ\else\textdegree\fi{} indicates that the reaction does not derive from a single state, but from a mixture of at least two interfering states of different parity.