[Halld-pid] Time-of-Flight Meeting Minutes, May 5, 2015

[Mark Ito]

Folks,

Please find the minutes below and at

https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_May_5,_2015

   -- Mark
___________________________________________________________


GlueX TOF Meeting, May 5, 2015, Minutes

Present:

  * *FSU*: Hussein Al Ghoul, Paul Eugenio, Sasha Ostrovidov, Aristeidis
    Tsaris
  * *JLab*: Mark Ito (chair), Simon Taylor, Beni Zihlmann


Announcements

The run is over, but all detector systems are turned on in the Hall. 
Beni reports that last night cosmic data was taken. Further data taking 
is not anticipated, but a decision to turn everything off has not been 
made either.

Calibration

Structure of Constants

Simon gave an overview of the current calibration scheme. Mike Staib has 
put channel-by-channel constants into the TOF/timing_offsets table. 
These equalize the times between TDCs and ADCs for each channel. We 
would like to put TDC-derived constants into this table. The TDC-ADC 
time offsets will appear in the TOF/adc_timing_offsets table. Mike 
scheme will calculate a global offset between the TOF and the rest of 
the detectors. This scheme should be independent of whether we use the 
JLab-style constants or the FSU-style constants for timing_offsets.

The next step for implementation is to talk to Mike and get his buy-in 
on the plan. Simon will do that.

FSU Status

Sasha continues work on the timing constants for the Spring 15 data. 
Recall that the fitting scheme suffered from a large level of background 
hits. He is now trying to isolate good hits by requiring a match with a 
charged track. The background situation improves, but does not go away. 
He is also experimenting with timing cuts to purify his sample.

JLab Status

Beni has started looking at timing calibrations constants for the 
single-ended counters. He uses events that have coincidences between the 
counter of interest and the common reference counter in the other plane.
He has also started looking a the energy calibration. He is selecting 
events where the hit is near the center of the counter judging from 
end-to-end timing (he is using ±0.5 ns for now). He plans to do this 
for several regions of each counter, not just the center.
Mark mentioned a scheme where the geometric mean of the energy is used 
for each counter. That yields a quantity that is roughly independent of 
position for each counter and may give higher statistics by allowing 
inclusion of all double-ended hits.

Time Bin Calibration

We discussed the idea of doing a time bin calibration on the CAEN TDCs. 
The goal is to equalize the size of the time bins associated with the 
four TDC devices used in each read-out channel of the device. Bryan 
Moffit has recently given us new driver software that will allow us to 
make the adjustment. Sasha did the calibration for the TDC at FSU. Beni 
has already looked at the variation in bin width for a few channels, he 
sees variation of 5 to 10%, consistent with what Sasha has seen at FSU. 
We did not make a detailed plan, but agreed to discuss the issue at 
future meetings.

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