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Qweak scintillator prototype cosmic test (5)
A. Summary of the cosmic test to estimate the number of photoelectrons of L and R PMT.
I. Determine the distance between pedestal peak and the single pe peak (in number of adc channels) of L and R PMT, with the following set-up.
(a) When checking the R PMT, move the T and B paddles to above L PMT lightguide with a V-shape layout. Two paddles are 10 cm apart vertically. (move the paddles to above R lightguide when checking the L PMT)
(b) Trigger = T. and. B
(c) Threshold of T and B paddles are set to 200 mV to reduce the pedestal to single pe peak ratio.
(d) Pedestal = 120, HV of L and R PMT = 2250 V (I reduced the pedestal from 180 to 120 and raised the HV from 1950 to 2250 V, to increase the separation between the pedestal and the single pe peak)
(e) L was in adc channel 1, R was in adc channel 2. I moved R to adc channel 5 to remove cross talk. Setting (d) and (e) cleaned up the ADC histograms.
Below are the ADC histograms of two cosmic runs with the above set-up.
(1) ADC histogram with paddles above the L lightguide. For R PMT, the pedestal peak is at channel 74, and the single pe peak is at channel 93. The distance is 19 channels.
(2) ADC histogram with paddles are above the R lightguide. For L PMT, the pedestal peak is at channel 53, and the single pe peak is at channel 93. The distance is 40 channels.
II. Took another cosmic run. The set-up of this cosmic run is the same as above, except that the two paddles were moved to Z=110 cm along SCIN Bar (Y=center) with a normal V-shape layout (one on top of the SCIN bar, and the other below the bar).
ADC histogram of this run. The minimum ionizing muon peak is at channel 2500 for L PMT, and at channel 1540 for R PMT. The number of photoelectron of L PMT = (2500-53)/40 = 61. The number of photoelectron of R PMT = (1540-74)/19 = 77.
B. Right now, with the above set-up, a few cosmic runs are being taken at different Z positions around SCIN bar to check the position depdendence of ADC and TDC response of L and R PMT.