The Final State Interaction And Decay Contributions To Hyperon Polarization In High Energy Reactions

Spin effect in high energy reactions is powerful tool to study the properties of strong interaction .Since the polarization of final-state hyperon can be measured easily through the angular distribution of its decay products in experiment, hyperon polarization is of the significance in many issues of the high energy spin physics, the study of hyperon polarization in high energy reactions has became one important aspect of spin physics. The study of hyperon polarization can provide important information about hadronization mechanism and the structure of hadron. In all study of this aspect, we can only measure final-state hyperon which is somewhat different with directly produced hyperon in colllisions in high energy reactions experiments. There are two factors contributing to the properties of the hyperon: hadron decay and final-state interaction. When we study hadronization mechanism through hyperon polarization, we must firstly consider about this two factors. This thesis will study them.At present, contributions to hyperon polarization derived from hadron decay have been argued, but in this argument decay polarization transfer factor is assumed as a constant usually. However, this thesis's analysis shows that spin transfer factor should depend on momentum of the hypron in both weak decay and electromagnetic decay. We derive decay spin transfer factor depending on moving direction of the final-state hyperon by calculating hyperon decay angular distribution including polarization correlation in mother-particle static frame system. The result shows that decay spin transfer factor strongly depend on moving direction of final-state hyperon.Contribution to hyperon polarization from interaction between final-state hadron is important, especially in high energy heavy-ion collisions, since the number of hadrons produced is very large, the effect can not be neglected much more. The study of hyperon polarization along the direction opposite to the reaction plane in the resent paper make the effect is much full of practical significance. Since final-state handron is composed of π meason mostly, for the sake of simplification, we focus on mainlycontributions to A hyperon polarization from final-state πA scattering in this thesis, and give analytic result after making use of effective chiral invariant Lagrangians to calculate cross section with fixed reaction plane. The result shows that initial-state unpolarized hyperon will be polarized along the direction opposite to the reaction plane through final-state interaction.