Quasi-elastic knockout of pions and kaons from nucleons by high-energy electrons and quark microscopy of “soft” meson degrees of freedom in the nucleon

Abstract

Electro-production of pions and kaons at the kinematics of quasi-elastic knockout (which is well known in the physics of atomic nucleus and corresponds to the t-pole diagram) is proposed for obtaining their momentum distribution (MD) in various channels of virtual decay N → B +π, B = N , ∆, N * , N * * , and N → Y +K, Y = Λ, Σ. It is a powerful tool for investigation of a quark microscopic picture of the meson cloud in the nucleon. A model of scalar qq ( 3 P 0 ) fluctuation in the non-trivial QCD vacuum is used to calculate pion and kaon momentum distributions (MD) in these channels. 1 In the constituent quark model the pion charge radius includes contributions both quarks and the ρ-meson pole (the vector meson dominance model): [< r 2 π > ch ] 1/2 = [3b 2 π /4 + 6/m 2 ρ ] 1/2 ≃ 0.68 fm.

10.1007/s11450-008-3013-4

“…4) The wave function for a nucleon having a spin projection σ and an isospin projection t has the form [19] …”

“…In this analysis, we employ experience previously gained by our group in developing (on the basis of the quark microscopic approach) the theory of quasielastic meson knockout by electrons in processes belonging to the N (e, e π)N or N (e, e K)Λ type and featuring longitudinal and transverse virtual photons [19,20] and also rely on a quark microscopic description of q 4q states. Owing to the simplicity of the mechanism of such reactions, a comparison of differential cross sections for processes involving the knockout of different mesons makes it possible to determine the structure of B states, including wave-function components corresponding to hidden strangeness (ss), and to find, for example, the parity of a B state from the shape and magnitude of the momentum distribution in B → N + M virtual decays.…”

“…A normalization of momentum distributions provides directly the spectroscopic factor [19,20], which is an important structural feature of the corresponding process. In the case of the pentaquark state of the spectator baryon, the spectroscopic factor is determined by the projection of the pentaquark-state wave function onto the meson-nucleon channel.…”

The exclusive reaction of pion quasi-elastic knockout from nucleon p(e, e′ π)B to various states of the final baryon-spectator B and the quark models for the pion cloud of nucleon

“…We carried out our calculations in the laboratory frame [7,10,11]. This enabled us, in particular, to preserve the variable k in the momentum distributions Ψ πB N ( k), which was a characteristic feature of the nonrelativistic theory.…”

“…The specific physical features of this process are discussed in our papers [10] and its formal microscopic theory is developed by Obukhovsky et al [7,11].…”