1. PCAL Cosmic Ray Tests Progress Report C. Smith μ U V W MODULE 2
Gegham Asyran (YerPhI)
Sergey Boyarinov (JLAB)
Shloka Chandavar (Ohio U)
Nerses Gevorgyan (YerPhI)
Yeranuhi Ghandilyan (YerPhI)
Ken Hicks (Ohio U)
Sergey Pozdnyakov (JLAB)
Ani Simonyan (YerPhI)
Stepan Stepanyan (JLAB)
Hakob Voskanyan (YerPhI) μ U V W
MODULE 2

2. Review of Module 1 Feb 12 – Mar 16: 141 runs , ~4 GB ntuples.
Shakedown of electronics and trigger.
Replaced all three 1881 ADCs (dead chans.).
Replaced four V895 discriminators (dead chans., DC offsets).
All signal and HV cables (576 total) work.
Replaced 1 patch cable out of 384.
Replaced 3 PMTs due to 60 Hz noise/instability.
80% of data taken with improperly timed ADC gate.
Evaluated gain matching methods.
Measured light attenuation in scintillating fibers.
Preliminary estimate of light yield.

3. Gain Matching
Vertical MIP muon deposits ~10 MeV in 5 scintillator stack.
Measured light depends on x due to fiber attenuation. μ x
For each PMT, measure light as function of x, then extrapolate to x=0 to get PMT gain.

4. Gain Matching μ x
For each PMT, measure light as function of x, then extrapolate to x=0 to get PMT gain.
To determine x, use strips in other views to localize hit.

5. Gain Matching μ U66 x W PMTS Non-vertical tracks dominate trigger
For each PMT, measure light as function of x, then extrapolate to x=0 to get PMT gain.
To determine x, use strips in other views to localize hit.

6. Gain Matching μ U66 x W PMTS Only 1 U strip fired
For each PMT, measure light as function of x, then extrapolate to x=0 to get PMT gain.
To determine x, use strips in other views to localize hit.
To reject non-vertical hits, use adjacent strips to veto.

7. Gain Matching μ U66 x W PMTS Only 1 W strip fired
For each PMT, measure light as function of x, then extrapolate to x=0 to get PMT gain.
To determine x, use strips in other views to localize hit.
To reject non-vertical hits, use adjacent strips to veto.

8. Gain Matching μ W59 U66 W35 x W15 Only 1 W strip fired
Only 1 U strip fired
Efficiency ~5%
For each PMT, measure light as function of x, then extrapolate to x=0 to get PMT gain.
To determine x, use strips in other views to localize hit.
To reject non-vertical hits, use adjacent strips to veto.
In practice use Level 3 filter to limit multiplicity to 1 for each U,V,W view.
Fit gaussian to each x slice to determine MIP peak.

9. Typical MIP distributions for U PMTs (W59 slice)
Vertical red line is ADC channel 200.
Calibration 20 ch./MeV

10. Initial result – non-exponential attenuation
Does not agree with bench measurements.

11. Solution ADC gate width too narrow
Increased to from 100 to 150 ns to accommodate long tails.
ADC gate timing late.
Gate timing determined by earliest PMT - complicated function of geometry in PCAL.
Simplified trigger to remove 30 ns of delay.
Trigger is now OR of W PMTs only. Still use Level 3 filter to select events with only 1 hit per U,V,W side.

12. After ADC gate adjustment

13. Mean ADC response vs position
Some periodic behavior in spatial response noted

14. Periodic behavior in ADC repsonse1 2 1 3
For example, differences in light collection for muons passing between fiber bundles (2) or on the outside (1) may be detected.
Or between scintillators (2) vs (3) for double readout strips.
Due to different number of U,V,W strips (68,62,62) there is a 68-62=5 channel modulation in the overlap of pixels and strips (beat frequency). This creates small sampling regions which may detect different efficiencies of light collection.

15. Periodic behavior in ADC repsonse1 2 1 3
For example, differences in light collection for muons passing between fiber bundles (2) or on the outside (1) may be detected.
Or between scintillators (2) vs (3) for double readout strips.
Due to different number of U,V,W strips (68,62,62) there is a 68-62=5 channel modulation in the overlap of pixels and strips (beat frequency). This creates small sampling regions which may detect different efficiencies of light collection.

16. Summary of HVs used to gain match PMTs
If intrinsic gain of PMTs were known, this might tell us something about light yield.

17. Estimate of absolute light yield
Preliminary estimate of light yield from Run 4057.
HV on PMT U66 was increased from 832V to 1000V to allow single photoelectron region to appear in ADC.
Sparcification threshold on this channel was lowered from 15 to 2 channels.
What appears to be the s.p.e. peak is seen channels 7-8, while the MIP from muons shifted from channel 200 to ~ channel 850.
The MIP peak represents a deposited energy of 10 MeV (5 strips/stack, dE/dx ~ 2 MeV/cm)

18. Modules 1 vs. 2 – Mean ADC vs position

19. Module 2 – Gain stability over 5 days

20. Module 2 – Gain stability over 5 days

21. Goals for Module 2 Multi-hit TDC data.
Adjacent strip x-talk, timing resolution.
Light coupling stability (wiggle phototube housings, re-measure gain).
How to measure light yield for all channels?
Next major challenge is setting up CLAS12 DAQ, testing flash ADC energy sum firmware, cluster finding, lookup table for attenuation corrections, etc. (Module 4?).