[Halld-pid] Start Counter Meeting Minutes, March 23, 2017

[Mark Ito]

Folks,

Please find the minutes below and at 
https://halldweb.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_March_23,_2017#Minutes 
.

   -- Mark
______________________


    Minutes

Present:

  * *FIU*: Mahmoud Kamel
  * *JLab*: Thomas Britton, Mark Ito (chair), Simon Taylor

There is a recording of this meeting <https://bluejeans.com/s/7ITwj/> on 
the BlueJeans site <https://jlab.bluejeans.com/>.


      Calibration Update

Mahmoud showed the latest results 
<https://halldweb.jlab.org/talks/2017/SC_Meeting_03-23-2017.pdf> from 
his time-walk calibration.

  * He showed plots of pulse-height (in ADC counts) vs. z-position (as
    measured by charged tracks) at the point of intersection with the
    start counter. Clear minimum ionizing peaks are visible with
    amplitude increasing with increasing z.
  * He then showed the difference in TDC time and ADC time as a function
    of pulse-height (in ADC counts) and the time-walk correction he
    derives from these plots. He then showed the same TDC-ADC time vs.
    pulse-height plot after the correction is applied. The pulse-height
    dependence is largely removed, as expected. In particular, there
    does not appear to be a large failure of the correction at large
    pulse-height.


      Propagation Time Correction Constants

Although there was no smoking gun in the time-walk calibration, Mark 
thought that, at least for now, we should go with the single-linear fit 
in the nose region to for the propagation time correction until that 
non-linearity is understood. The current constants being used in the 
monitoring run are consistent with that.


      Time-dependent geometry adjustments

We discussed a few issues:

  * Although the start counter is mounted on the target cart its
    position is physically tied to that of the target. In the HDDS
    representation, the two positions are specified independently.
      o Simon reported that that the target position has varied from
        run-to-run by as much as a centimeter. The cause of such a large
        shift needs to be understood, mechanically.
  * We discussed whether or not target/start-counter position should be
    reflected in the base geometry or represented as a correction in the
    new geometry specification scheme, i. e., what is the philosophy for
    deciding which shifts are considered part of the base geometry and
    which are called a correction.
  * Thomas pointed out that if we settle on a philosophy for the
    parametrization, that philosophy should be applied for all detector
    groups. It would be messy if different sub-systems viewed the base
    geometry in different ways.
  * Lately only Richard and Simon have been modifying the main GlueX
    geometry files.

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.jlab.org/pipermail/halld-pid/attachments/20170323/65ceca4d/attachment.html>