[Halld-pid] Time-of-Flight Meeting Minutes, June 30, 2015

[Mark Ito]

Friends,

Find the minutes from yesterday's meeting below and at

https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_June_30,_2015#Minutes 
.

   -- Mark
_______________________________________________________


GlueX TOF Meeting, June 30, 2015, Minutes

Present:

  * *FSU*: Hussein Al Ghoul, Paul Eugenio, Sasha Ostrovidov, Aristeidis
    Tsaris
  * *JLab*: Eugene Chudakov, Mark Ito (chair), Simon Taylor, Beni Zihlmann


Announcements

  * Beni announced a new policy for official drawings at the Lab. Access
    will be by request only in the future. Eugene mentioned that there
    may be an exemption for specific drawings so that they can be posted
    on the web.
  * Yesterday at the Physics Meeting, Paul Mattione showed plots of β
    vs. momentum using the TOF that showed clearly separated pion, kaon,
    and proton lines.


Calibration, FSU

Sasha showed some plots from his work using cable reflections to obtain 
time-walk corrections. See his webpage 
<http://hadron.physics.fsu.edu/%7Eostrov/tof/20150630/> for details.

In the time difference between two pulses in a given channel in the CAEN 
TDCs, he sees two peaks, one at 150 ns separation and on at 190. These 
two peaks are present for all channels. The time difference between 
successive peaks in the FADC shows a single peak at 190 ns separation. A 
plot the FADC two-pulse separation vs that of the TDC shows that these 
peaks are spurious, probably due to reflections, thought the rich 
structure seen is hard to understand. Sasha also showed various plots 
looking for a dependence on the pulse separation with FADC amplitude. He 
had hoped that this dependence could be used as the basis for time-walk 
corrections. The lack of a clear dependence on FADC amplitude makes this 
look hard to do.

Calibration, JLab

Beni showed results in two areas.

Attenuation Lengths

Beni has studied attenuation lengths on a counter by counter basis. He 
fits the pulse integral for a single end in the FADCs in bins of 
position along the counter as measured by TDC time difference. The 
resulting points are fit to two exponentials. The short attenuation 
length is about 76 cm and the long one is around 500 cm. He showed the 
distribution of these attenuation lengths separately. See his wiki page 
<https://halldweb.jlab.org/wiki/index.php/ADC_data#ADC_data:_Attenuation_length> 
for details.

FADC time differences vs. TDC time differences

Beni sees the expected correlation between end-to-end time difference 
measured by the TDCs vs. that measured by the FADC. However the relation 
has a measurable non-linearity; he parametrized this as a sine (in the 
region around 0 a linear function at lowest order). The reason for the 
non-linearity is not understood at present. Again see his wiki page 
<https://halldweb.jlab.org/wiki/index.php/TOF_Timing_TDC_vs_ADC> for the 
plots.

Automating the Calibration

Mark brought up the issue. We still have work to do on this front. The 
current constants are produced with a well-defined procedure but not 
easily automated in its current form.

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