PHENOMENON OF A DEUTERON (~- HYPERON) SPIN OSCILLATION AND ROTATION AS A METHOD OF THE N-N (QUARK-QUARK) SCATTERING AMPLITUDE INVESTIGATION V.G.BARYSHEVSKY, K.G.BATRAKOV AND S.L.CHERKAS Nuclear Problems Institute, Minsk, Belarus. We consider the effects of the deuteron (~- hyperon) spin rotation and oscillations at the matter which is proportional to the real part of the spin-dependent forward scat- tering amplitude. That gives a possibility of a direct measurement of this quantity. Spin- dependent forward scattering amplitude of the polarized deuteron (~- hyperon) on an unpolarized proton is determined by the nucleon-nucleon (quark - quark) rescattering, nonsphericity of the deuteron (~- hyperon) and spin-dependent nucleon-nucleon (quark- quark) scattering amplitude. Thus spin oscillation phenomenon represents a method for N-N (quarkoquark) scattering amplitude investigation, including its real part, over a broad energy range. 1 Introduction The most fundamental principles of our understanding of particle physics are an- alyticity and unitarity. Through analyticity we can get dispersion relation between the real and imaginary parts of the forward scattering amplitude. Experimental checking of dispersion relations is of great importance. While the imaginary part of zero angle amplitude is expressed through the total cross section using unitarity re- lation the measurement of the real part presents difficulties. The traditional method of measurement of the real part of nuclear scattering amplitude utilizes interfer- ence with the presumed known Coulomb amplitude dominating at small scattering angles. For measuring the elastic scattering cross section over such a small range of the momentum transferred the special methods based on the spectrometry of the recoil nucleons are applied. It is need to avoid rescattering by target for the accurate measurement of the momentum and the angle of the recoil nucleon. It has been shown in [1, 2] that there is an method which makes direct measure- ment of the real part of the spin dependent forward scattering amplitude possible. This technique based on the phenomena of particle beam spin rotation and oscilla- tion in a matter [1, 2] uses measurement of spin rotational angle under the condition of a transmission experiment -- the so-called spi n rotation experiment. For the particles with spin S _> 1 the spin oscillation and rotation exist even in unpolarized targets and its value does not decrease with particle energy grows [1, 2, 3] at high energies. Spin rotation and oscillation can be described by the particle spin-dependent refractive index of a medium which is proportional to the forward scattering am- plitude by a target particle. For particles with spin S > 1 (f~--hyperon, deuteron) forward scattering amplitude by an unpolarized nucleon has the form: F(0) = To + T2(Sn) 2 , (1) Czechoslovak Journal of Physics, Vol. 50 (2000), Suppl. 51 165