Version 4.02

Spectroscopic study of $\Lambda$ hypernuclei
up to medium-heavy mass region
through the (e,e'K$^+$) reaction
( Update to the conditionally approved E97-008 )

O. Hashimoto (Spokesperson)$^*$, S.N. Nakamura (Spokesperson), Y. Fujii,
H. Tamura, T. Takahashi, K. Maeda, H. Kanda,
T. Miyoshi, H. Yamaguti, Y. Okayasu, K. Tsukada


Department of Physics, Tohoku University, Sendai, 980-8578, Japan




S. Kato


Department of Physics, Yamagata University, Yamagata, 990-8560, Japan




H. Noumi


Institute for Particle and Nuclear Physics, KEK, Tsukuba, 305-0801, Japan




T. Motoba


Laboratory of Physics, Osaka Electro-Communication University, Neyagawa, 572-8530, Japan




L. Tang (Spokesperson), O.K. Baker, L. Cole, M. Christy, L. Gan, A. Gasparian, P. Gueye, B. Hu, C. Jackson, C. Keppel, Y. Sato, A. Uzzle, L. Yuan, X.F. Zhu


Department of Physics, Hampton University, Hampton, VA 23668, USA




J. Reinhold (Spokesperson), P. Markowiz


Department of Physics, Florida International University, Miami, FL 27411 USA




Ed. V. Hungerford, K. Lan, G.H. Xu


Department of Physics, University of Houston, Houston, TX 77204 USA




R. Carlini, R. Ent, H. Fenker, K. Garrow, D. Mack, G. Smith, W. Vulcan, S. Wood, C. Yan


Thomas Jefferson National Accelerator Facility, Newport News, VA 23606 USA




A. Ahmidouch, S. Danagoulian


Department of Physics, North Carolina A& T State University, Greensboro, NC 27411 USA




D. Dehnhard, H. Jungust, J. Liu


Department of Physics, University of Minnesota, Minnesota, USA




N. Simicevic, S. Wells


Department of Physics, Louisiana Tech University, Ruston, LA USA




M. Elaasar


Department of Physics, Southern University at New Orleans, New Orleans, Louisiana, USA




R. Asaturyan, H. Mkrtchyan, A. Margaryan, S. Stepanyan, V. Tadevosyan


Yerevan Physics Institute, Armenia




D. Androic, M. Planinic, M. Furic


Department of Physics, University of Zagreb, Croatia




T. Angelescu


Department of Physics, University of Bucharest, Bucharest, Romania




V. P. Likhachev


Department of Physics, University of Sao Paulo, Sao Paulo, Brasil

December 14, 2000





* Contact person


Osamu Hashimoto

Department of Physics, Tohoku University, Sendai, 980-8578, Japan
hashimot@lambda.phys.tohoku.ac.jp
Telephone 81-22-217-6452
Fax 81-22-217-6455






Proposal to JLAB PAC-19

Abstract

We propose to perform a spectroscopic study of $\Lambda$ hypernuclei for wide mass region using the (e,e'K$^+$) reaction. The expected results will provide $\Lambda$ hypernuclear spectra with the best energy resolution ($\sim$ 300 keV) ever achieved. An energy resolution of a few hundred keV and high statistical accuracy of the level structure will yield knowledge on the single-particle behavior of a $\Lambda$ hyperon in a medium mass nuclear system, and allow precise studies of the effective $\Lambda$-N interaction. The experiment will take full advantage of high quality electron beam at Jlab by introducing a new experimental geometry and a high resolution kaon spectrometer system now under construction.

The (e,e'K$^{+}$) reaction has unique characteristics as outlined below.

• A proton is converted to a $\Lambda$ hyperon.
• Spin-stretched states are populated with both spin-flip and spin-non-flip amplitude.
• Reaction spectroscopy with resolution as good as 300 keV (FWHM) can be realized.

The proposed experiment has two goals,

1. Excitation spectra of medium-heavy $\Lambda$ hypernuclei will be studied using the $^{28}$Si(e,e'K$^+$) $^{28}_{\Lambda }$Al and $^{51}$V(e,e'K$^+$) $^{51}_{\Lambda }$Ti reactions. This will provide precision binding energies and widths for the $\Lambda$ hyperon in its various states in nuclear mass up to A=50. The new structures and/or spin-orbit splittings suggested by the recent $( \pi ^ + ,{\rm K}^ +)$ reaction spectrum in the medium-heavy hypernuclei can be fully investigated with unprecedented energy resolution.

2. Precision measurement of $^{12}$C(e,e'K$^+$) $^{12}_{\Lambda }$B will be used in order to study the detailed structure of a typical $p$-shell $\Lambda$ hypernucleus in a qualitative way. In particular, the precision spectrum of $^{12}_{\Lambda }$B can be compared to its the mirror symmetric hypernuclei, $^{12}_{\Lambda }$C, which was studied with high statistics but limited resolution by the $( \pi ^ + ,{\rm K}^ +)$ reaction.

This experiment can now be undertaken with some confidence due to the pioneering and successful E89-009 experiment, completed in the spring of 2000. We have made a through examination of this experiment, and propose a new experimental geometry for the (e,e'K$^{+}$) reaction. This geometry will reduce the bremsstrahlung count-rate in the electron spectrometer, which limited the production rate in the experiment, while preserving the resolution and increasing the signal rate. To increase the coincidence rate and improve the resolution a new high-resolution, large-acceptance kaon spectrometer (HKS) is under construction to replace the SOS spectrometer which was used in E89-009.

This proposed experiment will be the first of the series of studies we would intend to undertake using the new kaon spectrometer.