Evidence for virtual Δ++ knock-out from 9Be by 1 GeV protons

Isobar Configurations in the Ground State of Nuclei. Effective Polarization of an Isobar

“…The width of a free isobar is about 120 MeV, which corresponds to a lifetime on the order of 10 -23 s. A virtual isobar is formed in a nucleus outside the mass surface; therefore, the main mode of decay of a free isobar, N   , accompanied by emission of a pion, is forbidden for it, which increases its lifetime in the nucleus. According to theoretical estimates [3-5] and the experimental data available at the present time [6][7][8][9][10], the admixture of isobar configurations in the ground state of the p-shells of nuclei calculated per nucleon amounts to several percent.…”

Momentum distribution of Δ-isobars in light nuclei with closed shells

“…The probability of the admixture of these exotic nuclear configurations is low because of a low nuclear density and a large isobar-nucleon mass difference. Attempts to detect the manifestation of the ∆-isobar configurations in the ground state of light nuclei were undertaken in series of experiments on nuclei with knockout of ∆-isobars initially present in the nuclei [7][8][9][10][11]. In this case, the reactions with knockout of a ++ ∆ isobar and its subsequent decay into the p + π -system with charge +2 are of interest to us.…”

Isobar configurations: ΔN correlations versus the independent particle model

“…Nuclear reactions that cannot be explained within a model that assumes a single interaction of a projectile particle with bound nucleons of a nucleus are an efficient tool in experimentally studying isobar degrees of freedom in the ground states of nuclei. As an example, we can indicate (π + , π − p) reactions [5,6], where the charged state of a scattered particle changes by 2e, or (p, p ′ π + p) [7] and (γ, π − n) reactions accompanied by the production of particles whose total electric charge is +2 or −1. Such experimental data are usually interpreted, using the model of the quasifree knockout of the isobar [5][6][7][8][9].…”