[Halld-pid] Time-of-Flight Meeting Minutes, August 9, 2016

[Mark Ito]

Please find the minutes below and at 
https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_August_9,_2016#Minutes 
.

_______________


    GlueX TOF Meeting, August 9, 2016, Minutes

Present:

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


      PMT Order

The order for the initial 25 PMTs has been issued as a PO. The order for 
an additional 6 is in the system, signed, and assigned a buyer.


      TOF rates during lumi scan

Beni looked at runs 11634-11637. He plots TOF rates as recorded by EPICS 
(per PMT) vs. electron beam current from the luminosity scan at the end 
of the Spring 16 run for selected paddles. Recall that paddle 1 to 19 
are regular width/length paddles, paddle 20 and 21 are narrow width long 
paddles and paddle 22 is a short single ended paddle.

The rates are in Hz as a function of beam current in nA. The data are 
from runs 11634 to 11637 where luminosity scans were done from 40 to 
140nA. The collimator was set to 5mm diameter and the radiator is 3x10-4 
with LH target full.

TOF PMT rates.gif 
<https://halldweb.jlab.org/wiki/index.php/File:TOF_PMT_rates.gif>

Beni noted that if the intensity goes up by a factor of five, the 
highest rate counters will be unusable. Mitigations: shielding? higher 
magnetic field?


      Cosmic data

Beni showed histograms of the mean time difference between paddle 21 of 
both planes, both for recent cosmic data at various voltages and for a 
run during this past Spring with the photon beam.

<https://halldweb.jlab.org/wiki/index.php/File:Tofres_1200V.gif>
1200V
<https://halldweb.jlab.org/wiki/index.php/File:Tofres_1250V.gif>
1250V
<https://halldweb.jlab.org/wiki/index.php/File:Tofres_1500V.gif>
1500V
<https://halldweb.jlab.org/wiki/index.php/File:Tofres_run11666.gif>
Spring '16, run 11666

There is not a marked difference in resolution between the various 
voltage settings for the cosmic data. However, all settings show poorer 
resolution and than the beam data. Clearly, the beam data has much 
better conditions for timing resolution measurements. If there is a 
trend in the cosmic data with voltage setting, it might be masked by the 
effect of the cosmic conditions.

Sasha suggested a position cut (time-difference cut) to ensure that the 
cosmic hits are coming from the "intersection" region defined by the 
crossed counters. This might clean things up for the cosmics. Beni will 
try that.

Beni also noted that although the gain on the inner counters has been 
reduced, he does not see any dead counters in the cosmic runs.


      Next Meeting

We will meet again in a week.

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  * This page was last modified on 9 August 2016, at 20:36.

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