7^th International Conference on Polarization Phenomena in Nuclear Physics

J. Phys. Colloques 51 (1990) C6-591-C6-594
DOI: 10.1051/jphyscol:1990680

PRODUCTION AND POLARIZATION OF STRANGE QUARKS FROM NUCLEAR MATTER : POLARIZATION OF Λ HYPERONS AT BACKWARD ANGLES IN THE REACTIONS πA→ΛX AND πA→ ΛK⁰ AT 4 GeV/c

I. ARAI¹, J. CHIBA², N. KATO¹, H. KITAYAMA¹, T. KOBAYASHI², A. MANABE², T. NAGAE³, Y. NAGASAKA¹, I. NOMURA⁴, V. PANTUEV⁵, M. SEKIMOTO³, M. TANAKA⁴, K. TOMIZAWA⁴ and K. YAGI<sup>4

1</sup>  Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305, Japan
²  National Laboratory for High Energy Physics, Tsukuba, Ibaraki 305, Japan
³  Institute for Nuclear Study, University of Tokyo, Tanashi, Tokyo 188, Japan
⁴  Institute of Physical and Chemical Research, Wako, Saitama 351-01, Japan
⁵  Institute for Nuclear Research of the Academy of Sciences of the U.S.S.R., Profsojuznaja 7a, Moscow 117 312, U.S.S.R.

Résumé
L'hypéron lambda est une sonde intéressante permettant d'étudier la production de quarks étranges et leur polarisation dans la matière nucléaire. Nous avons mesuré les polarisations et les sections efficaces différentielles des hypérons lambda produits sur cible de ¹²C aux angles arrières (70° < θ < 145°). Les polarisations ne sont pas reproduites du tout par un calcul basé sur une superposition de processus élémentaires alors que polarisation et section efficace sont bien reproduites par un modèle de quarks et de partons.

Abstract
A Λ hyperon is a fascinating nuclear probe at quark level. By using it, we can study the production of strange quarks from nuclear matter and their polarizations. Actually, we have measured the polarizations and the differential cross sections of Λ hyperons produced on ¹²C target at backward angles (70° < θ < 145°), where the production of Λ hyperon is strongly forbidden in the quasifree interaction of incident pions with nucleons in nucleus, using large-aperture spectrometer. The polarizations are not reproduced at all by calculation based on the superposition of elementary processes, while both the polarizations and the cross sections are reproduced well in calculation based on the quark-parton models. As a next step, we have just finished the experiment on ⁶Li target, which is also mentioned a little bit.

© EDP Sciences 1990