[Halld-pid] Time-of-Flight Meeting Minutes, July 14, 2015

[Mark Ito]

Folks,

Find the meeting minutes reproduced below and at

http://argus.phys.uregina.ca/cgi-bin/private/DocDB/ShowDocument?docid=2767 .

   -- Mark
___________________________________

GlueX TOF Meeting, July 14, 2015, Minutes

Present:

  * *FSU*: Paul Eugenio, Sasha Ostrovidov, Aristeidis Tsaris
  * *JLab*: Mark Ito (chair), Simon Taylor, Beni Zihlmann
  * *NU*: Sean Dobbs


Announcements

  * DAQ crates for the TOF have not been turned on in the Hall yet.


Calibration GlueX Note

We took a brief look at Beni's note 
<http://argus.phys.uregina.ca/cgi-bin/private/DocDB/ShowDocument?docid=2767>. 
In addition to producing the document Beni add comments to the code and 
rationalized some variable names. He also found an off-by-one bug in the 
paddle numbering and fixed it.
The last page shows a histogram of the time difference of mean times 
between the front and back planes, summed over all channels. The fit 
gives an RMS of 136 ps corresponding to 96 ps resolution in mean time 
per plane. This compares well to the TDR design goal of 90 to 95 ps.
ADC information is not covered in this note.
With the release of this note, Mark thought that it would be much easier 
to involve a student in the calibration process with the note serving as 
a road map. This would help us get a running start on new data from 
future runs. Paul will look into possible candidates.
Paul asked about the location of the code. It is in Beni's private area 
(home/zihlmann) of the Subversion repository. This started a discussion 
of a standard home for calibration programs. Such a convention would 
also need to accommodate scripts, ROOT macros, etc. Sean mentioned that 
we will discuss this issue at tomorrow's Calibration Meeting.

Calibration, FSU

Sasha reported on an alternate method for using cable reflections to 
extract time-walk corrections. In mode 8, the waveform data can be used 
to measure timing between the two pulses. He has identified a problem: 
the reflection is only clearly visible for large pulses and so is 
sitting on the tail of the main pulse. This shifts the effective 
threshold in the TDC in a way independent of time-walk. He is working on 
way to overcome this difficulty.

Areas for Future Work

Sean asked about the next steps now that we have an initial timing 
calibration. Beni told us that there was no more low hanging fruit in 
the time calibration. There are things like better functional forms for 
the timing fits that could be improved but are not likely to yield 
significantly better resolution.
The ADC calibration is still in progress; it remains on the list of 
things to do. For example, there are mysterious shifts in the position 
of the minimum ionizing peak as a function of position along the paddle 
after accounting for attenuation. Beni plans to return to it at some point.


      CAEN TDC Calibration

Sasha asked about the status of the calibration needed to equalize the 
size of the bins in the CAEN TDCs. Beni summarized:

  * Bryan Moffit has produced a library so that these constants can be
    downloaded.
  * Currently there are no constants (zeros) in the CAEN.
  * To start with we will write the values recommended by CAEN.
  * We need to ask Bryan if the code has a capability for read-back of
    constants.

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