2004 Fiscal Year Final Research Report Summary
Experimental research on partial restoration of chiral symmetry
| Project/Area Number |
15340069
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Particle/Nuclear/Cosmic ray/Astro physics
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| Research Institution | Tohoku University |
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Principal Investigator |
SHIMIZU Hajime Tohoku University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (20178982)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAZAKI Hirohito Tohoku University, Graduate School of Science, Assist.Prof., 大学院・理学研究科, 教授 (90260413)
KASAGI Jirohta Tohoku University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (10016181)
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| Project Period (FY) |
2003 – 2004
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| Keywords | chiral symmetry / scalar particle σ / mass shift / chiral transition |
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| Research Abstract |
The aim of this project was to search for precursory phenomena of the chiral transition in nuclei. Some experiments have been conducted at SPring-8, for this purpose, by utilizing a 2.4 GeV laser electron photon beam. A set of gamma detectors was employed in the experiments to detect multi-gamma events coming about with a nuclear target. The data analyses have been going on mainly on the following 4 processes :
1)γA→π^0π^0X
2)γN'→ωN, ω→π^0γ (N': nucleon in A)
3)γN'→π^0N
4)γp→π^0ηp.
We tried to find any signal concerning character change of the scalar σ having a close relation to the order parameter of the chiral transition in process 1). The ratio of 2π^0 invariant mass for the tungsten to the carbon target shows a larger value than 1 at the 2π threshold region, which may indicate a sign of partial restoration of chiral symmetry in the nuclear medium. However, there exist fake 2π^0 events coming from the 3π^0 channel. And a detailed analysis is underway. In process 2), the data show a bit of shift in the ω invariant mass distribution for low momentum ω events while the ω invariant mass stays at the right place for ω`s with relatively higher momentum. The φ-N cross section was obtained by measuring the A dependence of φ photoproduction cross sections. The obtained value σ_<φN> was rather larger than one in free space, suggesting that the φ properties might change in the nuclear medium..
In this project a new GeV γ beam line was completed and improved so as to provide a strong and stable tagged photon beam having an intensity of 3×10^7 photons/s.
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