Experimental Studies of Few-nucleon Systems at Intermediate Energies

Systems composed of 3 nucleons are a subject of precise experimental studies for many years. At the first stage the investigations were mainly focused on elastic nucleon-deuteron scattering, slowly extending to systematic measurements of the deuteron breakup reaction. Intermediate energies, below the threshold for pion production, deserve special attention: it is the region where comparison with exact theoretical calculations is possible, while the sensitivity to various aspects of interaction, like subtle effects of the dynamics beyond the pairwise nucleon-nucleon force, is significant. Moreover, the Coulomb interaction and relativistic effects show their influence in the observables of the breakup reaction. All these effects vary with energy and appear with different strength in certain observables and phase space regions, what calls for systematic investigations of a possibly rich set of observables determined in a wide range of energies. The next step in complication of the system are studies of reactions involving 4 nucleons-more sensitive, as expected, to subtle dynamics beyond the pairwise interaction. A brief survey of recent and planned experiments in the 3- and 4-nucleon systems is given.