Experimental Study of the H-particle

1991 Fiscal Year Final Research Report Summary

• Project/Area Number: 01044132
• Research Category: Grant-in-Aid for international Scientific Research
• Allocation Type: Single-year Grants
• Section: Joint Research
• Research Institution: Kyoto Sangyo University
• Principal Investigator: TAKEUTCHI Fujio Kyoto Sangyo University, Fuculty of Science, 理学部, 教授 (40121537)
• Co-Investigator(Kenkyū-buntansha): QUINN Brian Carnegie-Mellon University, Physics Department, Physics Dept, 教授 ; SCHUMACHER Reinhard Carnegie-Mellon University, Physics Department, Physics Dept, 教授 ; FRANKLIN Gregg Carnegie-Mellon University, Physics Department, Physics Dept, 教授 ; BASSALLECK Bernd University of New Mexico, Physics Department, Physics Dept, 教授 ; BARNES Peter D. LAMPF, 所長 ; EN'YO Hideto Kyoto University, Faculty of Science, 理学部, 助手 (30213606) ; TAKASHIMA Ryuichi Kyoto University of Education, 助手 (60163200) ; TAMURA Akio Okayama University, Faculty of Science, 理学部, 教授 (00025462) ; OKADA Kenji Kyoto Sangyo University, Inst. for Computer Sciences, 計算機科学研究所, 助教授 (90093385) ; MIYAKE Kozo Kyoto University, Faculty of Science, 理学部, 教授 (60025260) ; MASAIKE Akira Kyoto University, Faculty of Science, 理学部, 教授 (40022587) ; IMAI Kenichi Kyoto University, Faculty of Science, 理学部, 助教授 (70025493)
• Project Period (FY): 1989 – 1991
• Keywords: H-particle / Hypernucleus / Strangeness / Color magnetic interaction / XI stop events / AGS / Aerogel cerenkov counter / Quark degree of freedom

Research Abstract

The H-particle, predicted by Jaffe in 1977, is a quite unique object. The constituent two lambda particles are thought to be strongly bound only through color magnetic interactions. Therefore its existence is strongly related with the quark degree of freedom in nuclei.
The objective of this project was to carry out two experiments ; E813 and E836 at the newly-constructed large-intensity K-beam line at Brookhaven National Laboratory. In both experiments we aim at identifying the H-particle and determining its mass. In E813, the K^- beam is lead to the liquid hydrogen target, and the produced XI particle is stopped in the neighboring liquid deuterium target. The momentum of the recoil neutron from the XId->Hn reaction is measured. In E836, a liquid ^3He target is used instead. However the funding problem in US drastically reduced the running time of AGS accelerator, thus only one run of E813 could take place, before the end of this project.
We started the design of the detectors and test e xperiments at KEK. The construction of the new beam line at BNL was completed in summer 1990. Also the spectrometer magnet was installed at about the same time. The chambers, the acrogel cerenkov counters, the timc-of-fliglit counicr were built and tested. The doubic cryogenic target worked well too. The experiment E176 at KEK taught us that recoil protons are quite abundant from the target hit by K^-. So a newly added lucitc cerenkov counter was also installed.
However after the start up of the experiment in April 1991, the high voltage on the beam separators could not reach the designed value of 750 kV. We had to run the experiment at 600 kV, and this obliged us to run at 1.7 GeV/c beam momentum. This accident reduced the statistics of the result to about 6% of the expected number of events.
Immediately after the run in July 1991, the data analysis started. By November 1991, it was confirmed that all the detectors performed as expected, and the XI stop events are found. to be identifiable. This result was reported by P. D. Bames at the international symposium on the hypernuclear physics held in Shimoda in December 1991.
The data reduction is now in progress. But from that fact that the 1991 data lack the statistics, and an extension of E813 is approved at the PAC, and another run of 8 weeks starts in may 1992, we've decided to postpone the publication of the results until the new data are added to the existing ones.
The conditioning of the separators is now in progress. We can expect to run at 1.8 GeV/c this time. From this, and from the improvements in the trigger system, we expect to take about 170R H events this time, where R is the branching ratio of H production from the XId atom.
For the reason stated above, a publication is not yet ready, but we expect that to happen in the course of 1992.