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Polarization phenomena in the hypernuclear production reaction by the (7r+, K+) on 12 C and 13 C are studied within the framework of DWIA.We introduce the elementary amplitude for the (7r+, K+) reaction that is applicable to the DWIA calculation. By adopting the jj coupling model for nuclei, we investigate the effect of the distorted waves of mesons on the polarization of the hypernucleus '~C. and compare the present results with those obtained in the previous work. We also investigate the relation between the polarization and the analyzing power. § 1. Introduction 199Hypernuclei have been studied experimentally and theoretically since the first discovery of the hypernucleus on the emulsion. Most of the earlier works have been concerned with the separation energy of a hyperon and the spectroscopy of the hypernuclei. Recently, the nuclear reactions, (K-, ;rr-) and (;rr+, K+), have played important roles in studying structure of hypernuclei. The (K-, ;rr-) reaction produces what is called the substitutional states due to small momentum transfer to the target nucleus, while the (;rr+, K+) reaction excites many non-substitutional states due to the large momentum transfer to the target nucleus. As a result, they revealed properties of hyperon-nucleus potential such as potential depth and strength of spin-orbit term. Furthermore, these reactions allow us to study weak decay of hypernuclei: Since the hypernuclei produced by these reactions are generally polarized along the axis perpendicular to the reaction plane, nucleons and/ or pion emitted after decay of produced hypernuclei may show asymmetric angular distribution due to the parity violation of the weak interaction. The experiment for this purpose was done in KEK. 1 >.z> Another interesting subject related with this is the study of the electromagnetic properties, such as static magnetic moment and electromagnetic transition of hypernuclei. In these studies, it is essentially important to know the absolute value of the polarization of hypernucleus. It also deepens our understanding of the production mechanism of hypernuclei. Therefore, polarization phenomena of hypernuclear physics are important subjects to be studied. Unfortunately, it is not an easy task to determine polarization experimentally, since the hypernuclei are not stable. On the contrary, it is easier to measure analyzing power in the reaction. Although it is not related with the polarization directly except some specific cases, it may greatly facilitate our understanding of the reaction mechanism.In this situation, the purpose of the present paper is to study the analyzing power and the polarization of hypernucleus in the (;rr+, K+) reaction theoretically. Theoretical studies of the nuclear reactions have been based on the distorted wave impulse approximation (DW I A) so far. The t-matrix element of the elementary process for at

Abstract. Polarization of hypernuclei in (~, K) and (K, ~) reactions are studied by applying the semi-classical approximation to the transition amplitude. Simple formulas for the polarization of hypernuclei are obtained, and their validity is discussed in the reaction on the A = 12 system.

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