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User name mcnulty
Log entry time 04:04:47 on August28,2009
Entry number 286457
keyword=Larm HapDet alignment study
Larm HapDet alignment study.
1st picture comes from Ta target at 3pass, 20uA, run 24535. Top plot is focal plane distribution for s0 triggers. Bottom plot is same distribution at top with the black scatterpoints for events with good Hapdet ADC signal. The shadowed area shows outline of Hapdet. Note that this "white noise" spectra was not big enough to cover the entire focal plane, but it is the best we have so far. Also, there is a funny curvature to the lower edge of the HapDet shadow (maybe this is a result of track optics or rate bias?)
2nd picture comes from H2 target at 3pass, 1uA, run 24564. The superelastic edge is at x=~0.3m, the photocathode is at x=~0.6m (which gives a 30cm buffer). Note that the happex detectors are already positioned as far upstream as possible, thus to position the super elastic edge closer to the pmt would require decreasing the central HRS momentum Po.
For Hydrogen one can see that the highest rate spot is near x=0.2 and y=0.0; if one now looks at the Ta spectra with the Hapdet shadow, it seems that we are fairly well aligned, however it does seem that we may want to rotate the Hapdet to a slightly smaller angle (rotate clockwise slighly) and shift it to negative y very slightly.
It would be nice if we could illuminate more of the focal plane to find the full shadow of the detector.