Pion Meeting Dec 16 2022 3:30PM ET

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Zoom link: https://jlab-org.zoomgov.com/j/1608212513?pwd=M25LR1hzN3hLWm0xaFFETjZ0U1lQZz09

Agenda

Agenda:

1. Issues when simulating the experiments at Mainz Microtron (MAMI) (Elham)
2. Comparing the simulations with the beam test at Mainz Microtron (Elham)

Attendance

David, Elham, Kate, Neven, Simona M., Sudip B.

Minutes

1. Trying to reconcile signal size as seen from Mainz beam test data with G4 simulations. Using Poisson statistics, the widths of the signals seen in the beam test data indicate (https://dilbert.physics.wm.edu/Pion+Detector/85), https://dilbert.physics.wm.edu/Pion+Detector/86) a minimum of 75 PEs for typical runs (shorter lucite detector), with a "high-energy" tail to larger number of PEs. While this is a fine number for the experiment, we don't understand why this is so much less than the G4 simulation results, where present simulation predicts about 2300 PEs for the same 855 MeV electrons. This is a reduction factor of 0.033 to explain. Also not clear if we understand the gain of the PMT, if the 75 PEs factor is correct, and if we understand the ADC used at MAMI. With the 300 ADC channels for the peak above pedestal seen in the beam data and a quoted 25 fC/ADC channel, this suggests 7.5 pC peak pulse height. If this is really 75 PEs, then it implies a PMT gain of (7.5X10^-12C/(75X1.6X10^-19C) =6.2x10^5, which seems low. The PMT gain according the manual, for the ET R580 PMT/based package is 30x10^5 at 1500 V, so our numbers suggest a gain of a factor of 5 lower than this.
2. Changing the optical properties of the Lucite in the simulation does change the results, but not changing the PMT properties for some unknown reason. It seems suggestive that for some reason the photocathode efficiency is fixed at 100% for all wavelengths in the simulation.
3. Should we try to get hold of the QSIM code from ISU to see how the PMT is implemented there, since that code does very well with reproducing ShowerMax prototype data in simulation?
4. The dependence of the signal size on the arrival position of the track along the detector agrees (in relative terms) between G4 and data, suggesting that the optical properties (surface reflectivity and absorption length) of the lucite that are in G4 are reasonable.
5. Wouter explains that any reflections of optical photons from the photocathode are not counted as PMT hits in G4.
6. Simona has started dark box studies at JLab of the PMT model that is used in our prototypes, in order to calibrate the gain. Using a 300 Hz LED pulser, 20 ns wide pulse, readout out via FADC_250MHz (i.e. 4 ns samples), used 1730 V on the PMT. Not yet clear that we can identify the single PE peak.
7. Aside: prototypes used Tyvek wrapping and black tape for light-tightness, and optical grease to couple PMT to lucite. We expect to optical cement (same or similar to what QWeak used for Main detectors) in actual detectors.
8. Also need to understand the high-pulse tail seen in the data.