This is a followup to my previous post in which I plotted sensitivities in runs 6090 - 6904 to position modulation for the odd bars which have the Pb pre-radiators for the 4% US Al target and 3 mm raster. Figures 1 and 2 show data for the even bars that do not have the Pb pre-radiators. As pointed out by Dave Mack, the beam seems to have a narrower path to weave in x than it does in y and there is a possibility of collimator/plug misalignment in x. Figure 1 is a plot of sensitivities to position modulation in y as a function of beam (x,y). Once again, the sensitivities in y for y=0 are pretty well independent of x in the range -1 < x < +1 mm and are a little larger than for the odd bars. When the beam is moved in y by +/- 1 mm, sensitivities increase again by a large amount, this time an order of magnitude more than for the odd bars. Asymmetries are of opposite sign for opposite displacements in y, suggesting that the beam is hitting something visible to the bars. The sensitivities increase more when the beam is moved up compared to down. Perhaps the "golden" beam position is a little high. Figure 2 shows sensitivities for motion in x. The plots are mostly featureless, that is, all of the bars see much the same asymmetry, suggesting that variation of e-p cross-section and normal collimator acceptance with beam position are minor causes. Exceptions are beam positions at (1,0) and (0,1) where there is some variation with bar number. Asymmetries of opposite sign are seen here too at x = +1 and -1 mm.
Figure 1
Figure 2
