Hyperon Polarization In High Energy Hadron-hadron Collisions And Related Problems

Due to the discovery of a series of unexpected spin effects in such experiments, high energy polarized experiments have become a powerful tool for studying the structure of hadron and the properties of strong interaction. Since the polarization of J~p = 1/2~+ hy-peron can be easily determined be measuring the angular distribution of its weak decay-products, the measurement of hyperon polarization becomes an important aspect of high energy polarized experiment. In fact, the first unexpected spin effect was observed in experiments measuring hyperon polarization. The data show that the hyperon produced in unpolarized hadron-hadron or hadron-nucleus collisions is transversely polarized with respect to the production plane. There is no satisfactory explanation of this effect theoretically. Meanwhile, the azimuthal asymmetry of the produced hadron was observed in singly polarized hadron-hadron collisions, which is called single spin left-right asymmetry. In contrast to the leading order theoretical prediction at partonic level, which predicted zero asymmetry, the Jata show that the single spin left-right asymmetry is as large as 40% in the fragmentation region. These experiments are conceptually simple, the signals of the effects are clear, and the differences between the data and theoretical prediction are large. They provide an important place for testing QCD and developing the theory of strong interactions.In Ref. [10], the authors notice that the above-mentioned two striking spin effects, i.e., the hyperon polarization in unpolarized high energy hadronic reactions and the single spin asymmetry, are very similar both in the physical significance reflected by the phenomena and in the characteristics of the corresponding data. Inspired by these similarities, they proposed a new approach to understand these spin effects by relating them to each other. A physical picture is proposed and has been applied to pp → (?)X process. The obtained results are in good agreement with the data. The qualitative features of the polarizations of other hyperons and/or in other reactions have been also discussed and they are also...