PROTON (NEUTRON) SPIN ROTATION IN A POLARIZED NUCLEAR TARGET - METHODFOR INVESTIGATING NUCLEAR-INTERACTIONS

The nuclear interaction of a proton (neutron) beam of energy similar t o 1 GeV with a polarized nuclear target of length l results in spin ro tation of the incident particles through an angle theta=(10(-3)-10(-4) )l(cm). Using the spin density matrix method, it is shown that there a re two physically different mechanisms which lead to the spin rotation effect. The first mechanism, coherent spin rotation, has a quasioptic al nature and depends directly on the real part of a spin dependent pr oton-proton (pp) and proton-neutron (pn) forward scattering amplitude. It manifests itself in a broad energy range from a few hundredths of an eV [but for (pp) interaction, from tens of MeV] to hundreds of GeV. The second mechanism, diffractive spin rotation, is caused by Coulomb -nuclear interference in (pp) scattering and is of the same order as c oherent spin rotation in an energy region of about tens of MeV. The di ffractive spin rotation angle decreases with the incident beam energy, and, at about 1 GeV, it represents only 1% of the value of the cohere nt spin rotation angle. Experimental measurement of the spin rotation angle makes it possible to reconstruct directly the real part of the f orward scattering proton-proton and proton-neutron amplitudes. Spin ro tation is proposed to be used for the investigation of threshold effec ts and of resonant baryon states in the intermediate energy region.