Proposed experimental geometry

The E89-009 experimental setup accepted reaction electrons and kaons at angles down to zero degrees. The singles rates in each arm of electrons, positrons, pions and protons were analyzed and compared with theoretical calculations. However the calculated rates were renormalized to the experimental rates when used for the various estimates to be described below. It was found that the 0-degree electron-tagging method was limited by the accidental rate from bremsstrahlung electrons. We therefore propose to tilt the electron spectrometer by a small angle sufficient to exclude electrons from the bremsstrahlung process. This technique is described in detail in Appendix A.

A plan view of the proposed geometry, splitter+Enge spectrometer +high resolution kaon spectrometer (HKS), is shown in Fig. 9. Both the HKS spectrometer and the Enge spectrometer are positioned as far forward in angle as possible, without accepting 0-degree electrons or positrons. The HKS spectrometer, having a QQD configuration, was designed for the kaon arm. Details are found in the Appendix B. It has a momentum resolution of 2 $\times$ 10$^{-4}$ at 1.2 GeV/c, and a large solid angle of 20 msr, including the splitter. This is summarized in Table 2.

In designing the proposed experiment, data taken in E89-009 experiment were analyzed and singles rates of electrons, positrons, pions and protons in each arm were extracted. These are compared with the EPC code calculations and the normalization factors were derived. Assuming the obtained normalization factor for the hadron production rate at the forward angles, singles rates of the counters in the proposed setup were evaluated.

For the scattered electrons, the Enge split-pole spectrometer used for the E89-009 experiment will be adopted. However, the spectrometer is to be vertically tilted by 2.25 degrees so that the Bremsstrahlung electrons will not enter the spectrometer acceptance. The components of the focal plane detector system are redesigned and are explained later.

The splitter magnet has the same geometry used in E89-009 but the gap will be widened so that it matches the HKS geometrical acceptance.

The configuration and specification of the proposed hypernuclear spectrometer system is summarized in Table 2 and is shown in Fig. 9.

表 2: Experimental condition and specification of the proposed hypernuclear spectrometer system

Beam condition
Beam energy	1.8 GeV
Beam momentum stability	1 $\times$ 10$^{-4}$
General configuration	Splitter+Kaon spectrometer+Enge spectrometer
Kaon spectrometer
Configuration	QQD and horizontal bend
Central momentum	1.2 GeV/c
Momentum acceptance	$\pm$ 10 %
Momentum resolution ($\Delta p/p$)	2 $\times$ 10$^{-4}$
	(beam spot size 0.1mm assumed)
Solid angle	20 msr with a splitter
	(30 msr without splitter)
Kaon detection angle	Horizontal : 7 degrees
Enge split-pole spectrometer
Central momentum	0.3 GeV/c
Momentum acceptance	$\pm$ 20 %
Momentum resolution ($\delta p/p$)	2 $\times$ 10$^{-4}$
Electron detection angle	Horizontal : 0 degrees
	Vertical : 2.25 degrees