An analysis of run 8265 has been performed. Run 8265 was a field on profile run taken on July 21, 1994.
The analysis took two forms- firstly, the beam track (as reconstructed in the beam spectrometer) was extrapolated to the plane of EVBV. Second, events with one track reconstructed in the MPS spectrometer were selected, and the single track was extrapolated to the plane of EVBV. The beam profile is shown in Figure 1.
The fraction of the extrapolated beam contained within a given radius is shown in Figure 2, as well as the actual reconstructed tracks in the MPS. The dotted line is the extrapolated beam, the solid line is calculated from reconstructed MPS tracks. Recall that the MPS tracks will contain beam tracks, as well as elastic events, scatters, etc. In addition, we plot the expected pretrigger rate from a veto counter with a variable radius. The solid line is calculated from the reconstructed MPS tracks, the dotted line is just the extrapolated beam. The assumption is a 1.5 Megahertz beam.
We also looked at the expected deadtime from the pretrigger as a function of BV radius. We assume 3 microseconds deadtime per pretrigger, and a beam spill of 700 milliseconds and flux of 2 million particles over the spill. (Figure 3)
To conclude, we also looked at what fraction of events were vetoed by the previous BV, which you recall is a 6 inch by 4 inch counter. The old BV intercepted 98.5% of the extrapolated beam, and 95% of the reconstructed MPS tracks. This corresponds to a rate of 100K @ 2 MHz, which translates to a 43% deadtime. Remember that these deadtimes are only from the pretrigger, the total deadtime also includes readout deadtime.
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