GlueX TOF Meeting, May 31, 2016

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GlueX Time-of-Flight Meeting
Tuesday, May 31, 2016
11:00 am EDT
JLab: CEBAF Center, Room F326/327


  1. Announcements
  2. Review of minutes from the previous meeting
  3. Calibration Status
  4. mcsmear parameters
  5. NIM paper: svn co



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 .



  • FSU: Brad Cannon, Sasha Ostrovidov
  • JLab: Mark Ito (chair), Simon Taylor, Beni Zihlmann


Beni gave us an update.

He showed a plot of the difference in x as measured by tracks and as measured by the TOF (simply by noting which paddle was hit). The distribution is shown for each paddle in the plane.

Tof trkmatching.gif

In the TOF measurement, it is assumed that the paddles are 6 cm wide with no gaps. The slope seen in the plot is due to the known gaps between counters (wrapping, non-planar edges). A similar plot is shown for the difference in y. From this method Beni measures a gap of about 0.9 mm between the paddles. Simon is adding these gaps to the geometry. In the reconstruction, this will improve the matching to charged tracks.

The timing calibration is done for all spring 2016 data.

The plane with horizontal paddles is upstream in the experiment but downstream in the current geometry. Simon is fixing that by swapping the plane identifier: plane 0 becomes plane 1 and vice-versa.

Sasha and Beni have both noticed a trend where the matching has a lower efficiency near the beam line than in the periphery. The track matching efficiency is less than 95% in the central region.

Beni sees a issue with the difference between ADC and TDC timing in the central region.

T offset c17.gif T offset c22.gif

Each entry in the histograms is from calibration of a single run. The ADC-TDC time difference is a by-product of the time-walk correction. Shown is the mean difference in a run for two channels, 17 and 22. For 22, which is near the beam, there is a strange instability in the value. It is not known if this is related to the the matching inefficiency mentioned above. Sasha speculated that the effect may be due to small pulses around the beam line whose times are not well measured by the ADCs. Beni remarked that it is possible to check the quality of the ADC time before using it. A pedestal value of 0 indicates a problem finding a good time.

Beni has been talking to Sean about using the TOF calibration to determine the ADC vs. TDC time offsets rather than getting the numbers from Mike Staib's global program. The plan is to make the replacement.

The energy calibration using tracking and matched paddle hits is in progress.

Both of the geometry changes (plane order, gaps) will be put in for the reconstruction of Spring 16 data, which starts this Thursday.

NIM paper

Beni has started a draft. Find it in the Subversion repository. He asked the FSU folks to look over the construction section and expand it as necessary.

The plan is to distill parts of this paper and replace the current section of the TDR on the Time-of-Flight.

Meeting Frequency

We decided to try monthly meetings. That makes the next one on Thursday, June 28.