[Halld-pid] Time-of-Flight Meeting Minutes, May 31, 2016

[Mark Ito]

Folks,

Please find the minutes below and at https://goo.gl/CFkFcM .

   -- Mark
___________________________


  GlueX TOF Meeting, May 31, 2016, Minutes

Present:

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


      Calibration

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 
<https://halldweb.jlab.org/wiki/index.php/File: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 
<https://halldweb.jlab.org/wiki/index.php/File:T_offset_c17.gif> T 
offset c22.gif 
<https://halldweb.jlab.org/wiki/index.php/File: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 
<https://halldsvn.jlab.org/repos/trunk/publications/GlueXTOF>. 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.

Retrieved from 
"https://halldweb.jlab.org/wiki/index.php?title=GlueX_TOF_Meeting,_May_31,_2016&oldid=75433"

  * This page was last modified on 2 June 2016, at 13:51.


-- 
marki at jlab.org, (757)269-5295

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