Spontaneous Breaking of Chiral Symmetry and an Iso-singlet Scalar Meson

1993 Fiscal Year Final Research Report Summary

• Project/Area Number: 04804011
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 核・宇宙線・素粒子
• Research Institution: Yamagata University
• Principal Investigator: SHIMIZU Hajime Department of Physics Yamagata University Associate Professor, 教養部, 助教授 (20178982)
• Co-Investigator(Kenkyū-buntansha): FUKUNAGA Kiyoji Deparment of Physics Yamagata University Professor, 教養部, 教授 (70027035) ; KATO Seigo Department of Physics Yamagata University Professor, 教養部, 教授 (70013422)
• Project Period (FY): 1992 – 1993
• Keywords: Chiral symmetry / Precursor phenomena / Nuclear matter

Research Abstract

The aim of this research was to explore the existence of an iso-singlet scalar meson, sigma, having a mass of about 600 MeV by analyzing the data of the pi^0-pi^0 channel in the pi^-P->pi^0pi^0N reaction. We regarded this project as a "budding research" since our final goal was to catch signals of chiral symmetry restoration or those of precursory phenomena to chiral transition.
According to the result of the analysis up to date, a broad bump centered at around 600 MeV is observed in the pi^0-pi^0 invariant mass distribution. And the state corresponding to the bump is found to be a scalar by investigating the decay angular distribution in the rest frame of each pi^0-pi^0 event. It is mecessary, however, to carry out more detail analysis of the pi^0-pi^0 channel and to conduct an experiment to explore character change of hadrons in nuclear matter, in order to reveal whether the bump corresponds to the scalar meson originating chiral symmetry braking. Thus the first aim of this project as a "budding research" is attained.
We gave talks on the preliminary result of this research at the international conferences and the workshops shown in the preface of the report of research project, grant-in-aid for scientific research (C). Since then, we have received many questions, comments and encouragement from abroad through E-mail. We are planning to continue the analysis in more detail. On the other hand, we are preparing for an experiment proposed to INS, Tokyo University, using al GeV tagged photon beam to catch a signal from partial restoration of chiral symmetry.