Overview

The HKS-ENGE focal plane instrumentation is very similar to the one that has been employed in E89-009 (HNSS). During HNSS running, the electron arm (ENGE) rate was so high that each kaon event was associated with up to 8 electron events (within a reasonable coincidence time window). Therefore, a coincidence trigger was not feasible and the data acquisition (DAQ) has been triggered by the kaon arm alone. The HKS-ENGE system, however, will operate the ENGE spectrometer tilted out-of-plane with respect to the Splitter magnet. This will largely reduce the background rate associated with bremsstrahlung and M$\phi$ller electrons. The total electron rate should be no larger than 5 MHz. The hadron arm rate is assumed to be no more than 1.5 MHz (1 MHz $\pi^+$, 500 Hz K$^+$, and 0.5 MHz proton; see table 10). This will allow us to run the DAQ with an electron-hadron coincidence trigger. The total trigger rate should be kept below 1 kHz. Therefore, particle identification (PID) on the trigger level has to reduce the pion and proton rates by factors of $1 \times 10^{-4}$ and $5\times10^{-4}$, respectively. To reduce the likelihood of accidental kaon vetoes due to multiple tracks, the hadron trigger will be segmented. For example, an aerogel Cerenkov veto signal from a certain segment will only veto hodoscope triggers from scintillators in the same region of the focal plane.