Δ isobar in nuclei (review of experimental data)
Institute of General and Nuclear Physics, Russian Research Centre ‘Kurchatov Institute’, pl. Kurchatova 1, Moscow, 123182, Russian Federation
Experimental and elementary theoretical work relevant to the electromagnetic and hadron excitation of the Δ isobar in nuclei is reviewed. The historical development of the notion of non-nucleon degrees of freedom, from the quasinucleon and the pion to quarks and gluons, is described, and the role of Δ excitations is discussed. Gamma, electron, proton, pion, and ion beam methodologies and detector and target designs are discussed. Preliminary suggestions about γ, e, p, π excitation mechanisms are made. Problem areas that need more research are highlighted, and trends for the future and prospective experiments are discussed.