Analysis

BigBite Momentum resolution (for NIM paper)

Am am reanalyzing elastic data (1GeV, 2GeV, 3GeV) to get new plots of the BigBite resolution and offsets.

My old plot:

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My new plot:

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Offsets :

Need to correct small offsets for TgTh and TgPh. To correct TgTh offset I will introduce a -0.0015rad term to the HRSL optics matrix. To correct for the TgPh offset I will increase the zero-order Phi term in the BigBite optics matrix for 0.002734.

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Scaler problem

On Wednesday we were discussing strange behavior of the ratio of the gated BCM scalers (I call this ratio charge ratio). This ratio should be one and basically tells us, what is the amount of the accumulated positive (spin) charge relative to the collected negative (spin) charge. The result of my analysis was shown on the following figure. Please follow link:

http://descartes.ijs.si/~miham/e05102/MeetingNo76/Meeting1.png

On our meeting, we could not understand, where the observed oscillations (or asymmetry) came from. Therefore I decided to spend some time on this topic and try to understand what causes this kind of behavior. Now I believe I understand what is happening.

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First, please see figure above. This is the same picture as before, but without HWP correction. Blue squares correspond to BCM.u3 results. I have also added some lines, that show run numbers, where we inserted HWP (dashed lines) and where the target orientation was changed (full lines). For the plot of target spin orientation please follow link:

http://descartes.ijs.si/~miham/e05102/TargetFieldPolarization/TargetFieldOrientation.png

I realized that problems start at run #2700 where we changed the scalers for the first time. Please see the link:

http://hallaweb.jlab.org/halog/log/html/0905_archive/090524191328.html

Until that run we were using "negative" pair of gated scalers (Target, Helicity) = (-+) and (--), regardless of the target orientation. After this run we started to use "positive" pair of scalers (++), (+-). To confirm this assumption I made some additional analysis using HALOG end-of-run data and I realized, that problems happen only when the second pair of scalers (++), (+-) was used. For runs where pair (-+),(--) was used, ratio returned again to 1. Please see figures below, which show the charge accumulated by each gated BCM.U3 scaler and the final ratio between "positive" and "negative" accumulated charge.

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My explanation for this is, that we must have had a problem with one of the two gated scaler modules from the pair ( (++) or (+-)). To verify this, I made the same analysis using HRS-R BCM data. Result of that analysis are shown on figures below:

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From these plots you can see, that HRS-R scalers did not detect any jump in the charge ratio, which suggests that my strange results from Wednesday are most likely wrong due to the bad scaler module. I also remember, that we had multiple problems/encounters with double pulsing in the HRS-L scalers.

Now I would like to ask you, what do you think about this? Would you agree with my conclusions? Do you think that I should redo my BCM analysis using HRS-R data or is it enough to use good HRS-L data together with the HRS-R HALOG results?

Last modified: 11/23/11