[Halld-cal] [New Logentry] BCAL Cosmic data distributions

[dalton at jlab.org]

Logentry Text:
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In this log entry I show some distributions of the ADC values from the cosmic data taken over the weekend.  This is run 3086, /gluex/Subsystems/BCAL/data/south/bcal_s4_3086.0.coda

The figures show either the max sample height or the waveform integral.  All have been pedestal subtracted on an event-by-event basis using the first 10 samples of the waveform.  There are plots for the upstream BCAL channels, the downstream channels and the 4 PMTs on the two lower trigger scintillators.

The different layers (rings) have different distribution shapes because they readout detector cells of different cross sectional area.  Layer 1 is the most symmetric (most square, if you like) and thus should have the least dependence on the direction of interacting particles.  The longer cells of layer 4 could have approximately a factor of 4 difference in length to width and thus the signal component is wider.  The inner ring can therefore be used to get a crude global calibration.  Fitting a Gaussian and a Landau (see Fig. 7 for example) to the inner ring integral spectrum gives a most probably value of about 230 ADC samples for the US and DS ends together.  This value corresponds to approximately 22 MeV of deposited energy, thus the calibration factor is about 10e-4 to get GeV.  This was the existing global value in the analysis software.

Most of the events are pedestal since we readout all channels for each trigger.  As can be seen there is a significant pedestal width.  In layer 1 the peak from minimally ionising particles (MIPs) merges into the pedestal somewhat.  This is more aparent for the downstream end which is further from the trigger paddles and therefore has more attenuation in the detector fibers and also more aparent in the integral rather than the max, where the sensitivity to the pedestal is enhanced.

The trigger PMT signals are larger and are easily separated from the pedestal.  Clearly one scintillator produced significantly more triggers than the other.  The triggers in (roc 38, slot 4, channels 6 and 7) had 7 times as many triggers as (roc 38, slot 4, channels 4 and 5.)


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