(γ, 3π) Vertex and Double π⁰Photoproduction

Abstract

915Effects of the (r, 3rr) vertex in the reaction r+p-7 p+2rr 0 is studied. It is shown that the (r, 3rr) -part of the amplitude for this reaction is given by the " meson current part" of the amplitude for the single rrO production by a virtual photon, multiplied by a certain numerical factor including the effective coupling constant of the (r, 3rr) vertex. Thus referring to the theory of Fubini, Nambu and Wataghin for the single pion electroproduction, the (r, 3rr) -part of the double rrO photoproduction amplitude can be obtained almost exactly.It is also shown that, under appropriate experimental conditions, the major contribution to the reaction r+p--?p+2rrO comes from the absorption of the incident photons via the (r, 3rr) vertex, unless its effective coupling constant ,\ be much smaller than the value expected from the simple perturbation calculation. Thus, the experimental study of this reaction would possibly provide an alternative and rather unambiguous method for the determination of J.. An example for such a measurement is proposed, and the cross section under the proposed conditions is calculated. § I. IntroductionRecently, the (r, 3n) interaction or the reaction (1·1) has become one of the most interesting problems in the elementary particle physics. The problem has been raised mainly in connection with the theory of the isoscalar electromagnetic form factor of the nucleon 1 ) and the dis-covery2) of the various resonance states of pion systems. Also, in the second and third resonances of the pion photoproduction, the (r, 3n) vertex may play a decisive role 3 > analogous to the supposed role of the pion-pion interaction in the corresponding resonances of the pion-nucleon scattering. 4 > The effects of the (r, 3n) interaction in the various types of the elementary particle reaction have been theoretically examined and several methods for experimental determination of its interaction strength are proposed. 5 >-B> However, the problem is considerably delicate, and perhaps the conclusions expected from the methods thus far proposed can not be so conclusive.This is mainly owing to the expected smallness of the (r, 3n) coupling *l On leave of absence from Department of Physics, Tohoku University, Sendai. at UCSF Library and Center for Knowledge Management on March 21, 2015 http://ptp.oxfordjournals.org/ Downloaded from 916 K. Itabashi and T. Ebata constant A. *l In all the reactions that have thus far been considered for de-termination of A, the process via the (r, 3n) vertex is only a minor one, namely the most part of the total yields is the background to be subtracted. Thus, naturally one tends to consider the interference effects between the major processes and the process via the (r, 3n) vertex, since the interference effects are generally sensitive to the small admixture of the minor processes. However, by just the same reason, one cannot necessarily ignore the other minor processes, about which we have not so much information. Therefore, in general, the theoretical results cannot be so conclusive.As ...

The " -Exchange" Model for the Reaction + N -> N* +

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Effects of the Pion-Pion Interaction on Photonuclear Reactions

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