Pionic degrees of freedom in atomic nuclei and quasielastic knockout of pions by high-energy electrons

Abstract

Two kinds of virtual pions in the nucleus are discussed: delocalized pions forming a pionic condensate and pions localized in the pionic clouds of individual nucleons in the nucleus. The pionic degrees of freedom in nuclei may be efficiently verified in pion quasielastic knockout experiments A(e, e’π±)A*. First, the momentum distribution (MD) of collective pions has a bright maximum at K ≃ 0.3 GeV/c. Second, the excitation spectrum of the recoil nucleus is concentrated at low energies Erec, A ≃ K2/2MA≤1 MeV. The results for the pion knockout from mesonic clouds of individual nucleons in nuclei are distinctly different.