GlueX TOF Meeting, July 14, 2015

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GlueX Time-of-Flight Meeting
Tuesday, July 14, 2015
1:30 pm EDT (non-standard time)
JLab: CEBAF Center, Room F326/327


  1. Announcements
  2. Review of minutes from June 30
  3. Calibration Status FSU
  4. Calibration Status JLab



Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2015 on the JLab CUE. This directory is accessible from the web at .



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


  • 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. 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 Calibration 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.