Eur. Phys. J. A (2005) 24: 217-222
https://doi.org/10.1140/epja/i2004-10132-7

Original Article

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

Institute of Nuclear Physics, Moscow State University, 119899, Moscow, Russia

Received: 20 September 2004
Accepted: 28 January 2005
Published online: 11 March 2005

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 E _{rec, A} ≃ K ²/2M _A≤1 MeV. The results for the pion knockout from mesonic clouds of individual nucleons in nuclei are distinctly different.