GlueX Start Counter Meeting, March 24, 2016

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GlueX Start Counter Meeting
Thursday, March 24, 2016
10:00 am EDT
CEBAF Center, Room F326/327


  1. Announcements
  2. Review minutes from the last meeting
  3. Calibration Update
  4. Run Issues
  5. DAQ Tasks for Spring 2015 Commissioning Run
  6. Action Item Review




Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2016 on the JLab CUE. This directory is accessible from the web at .


The meeting came to order at 10:00 am.


  • FIU: Mahmoud Kamel, Eric Pooser
  • JLab: Mark Ito (chair), Simon Taylor, Beni Zihlmann
  • NU: Sean Dobbs


Beam delivery to Hall D is scheduled for Sunday, March 27.

Review minutes from the last meeting

  • No progress on the NIM paper or the TDR since the last meeting.

Calibration Update

Mahmoud gave an update on time propagation delay calibration focusing on a comparison between data and simulation. See his slides for the plots and details.

He showed the results of the calibration for each section of the start counter for a sample of recent data (run 10496) and the sim1 simulated data. Differences are seen mainly in the nose section, where fits do not represent the data very well.

The overall timing resolution is 270 ps for data, but 370 ps for simulation. To start with for simulation, there is 300 ps of smearing introduced by mcsmear but the reason for poorer resolution than that is unclear. Mahmoud may try to go back to a simpler propagation delay scheme that uses a constant velocity rather than the section dependent velocity (straight/bend/nose) that is the current default.

Resolutions in mcsmear

Sean showed monitoring plots again comparing data and Monte Carlo. He has collected a few interesting plots for other subsystems as well. The start counter section shows a large number of RF-bucket mis-identifications for simulation in the plots from which resolution numbers are extracted. The reasons are not clear; RF bucket selection for the data looks clean.

mcsmear parameters

We discussed the parameters used by mcsmear to introduce detector effects to the start counter hits. The first line in the table is the 300 ps mentioned in the discussion of Mahmoud's slides (above). Sean proposed using the measured values of the resolution as recorded in the CCDB to do time smearing with a channel-dependent width.

We discussed how the other parameters should be measured and indeed whether these are the best set of parameters to use. Mark and Simon will make a proposal on how the various effects should be parametrized and how those parameters should be measured. They will report back to the group at a future meeting.

Multiple ADC hits checks

Sean reminded us that now were are running with npeaks = 3 in the FADC-250s and there is a need to study the matching of ADC and TDC hits with this new scheme.

Efficiency measurement

Paul Mattione had commented on Mahmoud's presentation of start counter efficiency at the Calibration Meeting. There appears to have been some skepticism expressed due to the use of protons to measure efficiency. Mahmoud pointed out the he gets the same results independent of the particle species. We agreed to circulate Paul's points and Mahmoud's response and discuss the issues at the next meeting.

Run Issues

There was one round of pedestal adjustment for the FADCs early in the run by Eric and Sergey Furletov. Nothing has been done since. Beni advocates doing another round before we start running again, and not just for the start counter.

The meeting adjourned at 11:05 am.