Vertex Cut

Events that survive the cuts so far have a reliable vertex determination. In figure 5.19 the vertex distribution is shown for the events which have passed all the cuts described so far together with Monte Carlo events normalized to the total number of events. The vertex distributions agree. The data show a large peak around the nominal interaction point and another peak close to due to the proton satellite bunch. There are a few events with large which are probably due to remaining non e-p background in the sample. To remove these events we select events if .

Figure 5.19: The open histogram shows the vertex distribution for the Monte Carlo data after applying all the cuts up to the vertex cut. The data are shown as points with statistical errors. The Monte Carlo data are normalized to the number of data events.

Through this cut events are rejected and events remain. Scanning of the remaining events shows that no obvious non- e-p events are left in the sample.