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User name gilman
Log entry time 04:13:45 on October 2,2006
Entry number 186143
keyword=changed to aluminum at +2%
Guy, looking over the LH2 data, aooears to have found why our high Q^2 singles runs have a low Ge/Gm, though we do not understand evverything yet and could be misguided, The clue was in the aluminum 15 cm dummy run, which shows 4 peaks, as if we are hitting both 4 and 15 cm dummies. This suggests wither the target is mispositioned (which could be for dummies only) or the beam is wierd (notice the entries concerning funny spot++), or both.
So,,, perhaps we have a large aluminum background in the LH2 singles from the flow diverters?
GUy looks at the Al and LH2 spectra, and concludes ~1/4th of the
data scould be aluminum, and these events appear to have a smaller
Ge/Gm, ~0.5, in Q^2 = 0.5 data. He tries using reconstructed y_beam
to remove flow-diverter backgrounds, but this seems to have no effect.
(Thus, my simple model for what causes the background is likely wrong.) We decide to spend some time overnight measuring Al at the three deltas in this kinematics to allow something of a background subtraction, in case there is no cut we can apply to reduce the Al contamination.
There are several obvious things to try in replay, but not much else we can do in the limited time until the end of the run.