[Halld-pid] Start Counter Meeting Minutes, August 13, 2015

[Mark Ito]

Folks,

Find the minutes below and at 
https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_August_13,_2015#Minutes 
.

   -- Mark
   _____________________________________________________


    GlueX Start Counter Meeting, August 13, 2015, Minutes

Present:

  * *FIU*: Werner Boeglin, Mahmoud Kamel
  * *JLab*: Mark Ito (chair), Eric Pooser, Simon Taylor


      Review of minutes from the August 3 meeting

We went over the minutes 
<https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_August_3,_2015#Minutes>. 


  * Eric has started on the GlueX Note describing the calibration procedure.
  * For the time propagation correction he has decided to use the
    measured delays[?] rather than a set velocities with a different
    velocity for each region.
  * Eric updated the PID library to use the final versions of the
    calibrations. The CCDB has been updated as well.
  * The resulting time resolution is 60 ps below design for all 30 paddles.
  * Eric pointed out that a years has gone by since construction and
    there is no visible deterioration of counter performance. Recall
    that in the past degradation was apparent after a few months.


      Start counter efficiency calculations

Mahmoud presented slides describing how he determines efficiencies and 
how the method has improved from previous attempts. See his slides 
<https://halldweb.jlab.org/talks/2015/ST_efficiency.pdf> for details.

Simon pointed out that, unless explicitly turned off, there are a lot of 
tracks that get their t_0 from the start counter. For these tracks, the 
existence of start counter hit is therefore a given and the efficiency 
might be artificially high. Mahmoud will check whether this association 
between tracking and the start counter was on or off (off: USE_SC_TIME=0).


      Calibration

Eric gave us an update on the calibration effort, in particular the 
attenuation correction. For details see his slides 
<https://halldweb.jlab.org/talks/2015/ST_Calibration_Update_Aug_13_2015.pdf>. 


For work with the data he incorporated the path length correction and is 
now calculating dE/dx (literally). The distributions tighten up 
considerably. He has success fitting the distributions to Vavilov 
distributions. The problem with a lack of statistics at the upstream end 
remains however. He settled on using the attenuation values measured on 
the bench at FIU for the corrections.

With the updates to the PID library to apply all of the calibrations, 
Sean Dobbs asked about the plan for installing calibration constants in 
the MC variation. Eric has started looking at how the hits are created 
in HDGeant. The idea is to apply constants that reverse the process 
applied in event generation.

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  * This page was last modified on 14 August 2015, at 18:06.


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