General Procedure

The spectrometer optical calibration procedure is specially designed for HKS spectrometer system. It is somewhat different from other Hall C basic equipment experiment using only HMS and SOS, because of the existence of splitter magnet right after the target. This complicate both the angle and momentum calibrations.

The required calibration runs for HKS optical calibration are:

• Separate Enge and HKS sieve slit(SS) runs, using Carbon target without raster. Check the Enge and HKS focal plane correlations: $Yfp$ vs. $Xfp$, $Xpfp$ vs. $Xfp$, $Ypfp$ vs. $xdp$. Statistics is enough when all the bands can be clearly seen (see fig.4 and fig.5 for Enge, fig.6 for HKS).

• Two arm coincidence runs in production kinematics, on CH$_2$ target to obtain $\Lambda$ and $\Sigma ^0$ spectra. We also need data on Carbon target for the $^{12}_\Lambda$B ground state spectrum. The yield of $\Sigma ^0$ and $^{12}_\Lambda$B gs should reach at least 1500 events and 1500 events, respectively. We should also look at the S/A ratio under the $\Lambda$ peak to keep it more than 5 to 1 after raster correction.

The general procedure for the calibration is:

1. Separate Enge and HKS sieve slit calibration to obtain angle reconstruction matrices using original momentum reconstruction matrix.

2. Raster correction for CH$_2$ target data using existing raster correction matrix.

3. Kinematics calibration to find deviation of beam energy, Enge and HKS central momenta from their nominal values. The central angles of the spectrometers are not used in the missing mass calculation and they are not needed for fixed-angle spectrometer.

4. Two arm coupled momentum calibration to obtain momentum reconstruction matrix.

5. After getting the calibrated momentum matrix, go back to first step again to do SS calibration using the new momentum matrix. Iterate until best resolution is reached.