Single-paddle Delta(t) from cosmics at different HV
Setup
- Standard 100'', 6cm TOF paddle inside the black box in the FSU lab.
- Simple short trapezoidal light-guides (unlike the ones in TOF).
- Older 10534SEL PMTs with nominal gains of 1.6*10^6 and 1.2*10^6 @1750V.
- Trigger is a coincidence of 2 "finger" (1cm wide) counters positioned at the center of the paddle as shown here.
- JLAB discriminator at 30mV threshold.
- CAEN VX1290 TDC.
- No splitters.
- 2 measurements at different HV: at 1500V (1200 events) and at 1200V (800 events).
Efficiency
The efficiency is measured by counting the number of triggered events with a TDC hit in a proper time window for left and right PMTs independently and for both of them simultaneously.| Left | Right | Both | |
| 1500V | 93% | 82% | 81% |
| 1200V | 56% | 22% | 20% |
Delta(t) resolution
Delta(t) = (tleft - tright)/2. No timing correction is done for time-walks or anything else. |
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After HV reduction from 1500V to 1200V, Delta(t) resolution has changed by 26ps in sigma (from 161ps to 187ps), or by 17ps in RMS (from 214ps to 231ps). There was also a shift in the mean value by about 110ps. The reason for a non-Gaussian shape is unclear.
Old measurement from 2009
Measurements of the same paddle with the same PMTs in 2009 gave a resolution of 124ps. Note the proper Gaussian shape. The differences are:
- HV is at 1750V instead of 1500V or 1200V.
- F1TDC instead of VX1290.
- CAEN 812 CFD instead of JLAB LED (I guess this is the most important one).