As described in more detail at elog106 the Halo 4 rates recently have been large and erratic. The most recent time we appear to have had high beam current beam is Sunday evening at around 6 PM. The attached Figure 1 shows how the halo 4 rate varied over 1 hour at that time. For 140 uA beam, it varied from 10 kHz - 50 kHz. In contrast, I show an earlier one hour period in Figure 2; where the halo 4 rate was rock steady for one hour at ~ 5 kHz. (Both of these were done with hydrogen target and 3x3 mm^2 raster.) As detailed in the above elog, I cannot make an airtight case that this increased halo rate is impacting what we see in our main detectors. There are a long list of caveats about why an increased halo rate in this halo monitor might not matter for the experiment. But I think the difference is dramatic enough that it is worth asking accelerator to do some "health checks" on the beam tune tomorrow (Wednesday) morning before we launch into the long holiday weekend. One thing they can certainly do is standard harp scans to check the optics in the hall C line. I suspect Jay Benesch would have other suggestions of things to check.
Fig 1: Recent 1 hour Halo 4 rate plot
Fig 2: "Good" halo 4 rate plot from Nov. 15
