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Log entry time 13:46:24 on January 18, 2005
Entry number 139591
Followups:
keyword=More BigBite timing changes needed for Aux planeThe T6 stops peak for the E counters in BigBite can be used as a guidepost to predict where the E and Aux counters will be in the TDC spectra for triple coincidence T5 starts.
Run 1615, elastic scattering on deuterium, was taken just after the last HARDWARE change in the relative timing between T3/T5 and T6 gates. In that run, E counter stops for elastic deuterons (T3 trigger) appear 675 channels before the T6 trigger. If the T6 peaks is defined as "zero", then the T3 peak is at channel -675, or -23.6 ns. There are 3 quantities that are added or subtracted to that to get the T5 triple timing relative to T6:
- Relative time between T5 and T3. This adds 10 ns.
- Removing the deuteron time of flight. @432MeV/c, this subtracts 45 ns.
- Adding in the proton time of flight. 250MeV/c adds 39 ns, 550 MeV/c adds 20 ns.
Using the T6 trigger, the AUX counter stops have recently been observed to arrive 1400 to 800 channels before the T6 stops. Assuming the worst case of 1400 channels, the AUX counter stops are predicted to be at channel 40 for 250MeV/c, and channel -500 for 550 MeV/c. (It is actually not quite as bad for the high momentum, since the E-AUX difference will be less due to the faster protons.)
Since we want our TDC stops be at roughly 500 or more, we need to add 1000 channels (35 ns) to the AUX stops, or remove 35 ns from the overall BigBite start. Olivier believes that he can remove this much from the BigBite gate.
Whatever is done, the relative timing between ADC and TDC gates should be
preserved as that is correct.
A copy of this log entry has been emailed to: gayou@jlab.org
Predicted E counter stops for T5 trigger
Predicted AUX counter stops for T5 trigger
