Potential of quasielastic meson knockout from a nucleon by high-energy electrons and pions for studying the structure of exotic excited states of a final-state baryon

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The possibility of studying q4\( \bar q \) exotic baryon states by means of N(e, e’M)B reactions proceeding via an extremely simple mechanism and involving the quasielastic knockout of various mesons from a nucleon by electrons of energy in the few-GeV region is considered as a development of the previous investigations of our group. A quark microscopic formalism based on the cluster model of q4\( \bar q \) states, which makes it possible to determine momentum distributions of mesons in various channels of B → N + M virtual decays (in principle, these distributions can be compared with experimental data), is expounded by considering the example of the pentaquark (B = Θ+). The decay widths of the q4\( \bar q \) baryon states being discussed are governed by the degree of separation of quark clusters (this is a parameter of the model used). The electroproduction cross sections prove to be small because of kinematical constraints requiring that physically admissible values of the momentum ‖k‖ of the virtual meson M lie in the region where relevant amplitudes are suppressed substantially by form factors in pentaquark vertices. In particular, N (e, e′π±)B reactions involving pion knockout furnish direct information about nonstrange components of baryon B; however, the expected cross sections for such reactions are an order of magnitude smaller than their counterparts for analogous reactions leading to the production of a pentaquark Θ+. Because of the smallness of the electroproduction cross sections, it is reasonable to consider the production of a pentaquark and other q4\( \bar q \) exotic states in reactions characterized by quasielastic kinematics and initiated by pions of energy in the range between about 1 and 5 GeV and in similar stripping and pickup nuclear reactions.