[Halld-offline] HDGeant4 Meeting Minutes, May 4, 2021

[Mark Ito]

Folks,

Please find the minutes here 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_May_4,_2021#Minutes> 
and below.

   -- Mark

      _____________________________________


    HDGeant4 Meeting, May 4, 2021, Minutes

Present: Alex Austregesilo, Tegan Beattie, Sean Dobbs, Mark Ito (chair), 
Igal Jaegle, Richard Jones, Zisis Papandreou, Lubomir Pentchev, Simon 
Taylor, Nilanga Wickramaarachchi, Beni Zihlmann

There is a recording of this meeting 
<https://bluejeans.com/s/smXkAPjiI7L/> on the BlueJeans site. Log into 
the BlueJeans site <https://jlab.bluejeans.com> first to gain access 
(use your JLab credentials).


      Review of minutes from the last meeting

We went over the minutes from the meeting on April 6 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_April_6,_2021#Minutes>. 
Tegan will continue his studies using the software for analysis launch 
version 38 with its wider timing window, dropping back from version 40. 
He will get it running on the JLab farm.


      Simulating Hit Efficiency for the FDC

Lubomir presented Garfield studies 
<https://www.jlab.org/Hall-D/detector/fdc/FDC_tracking_Apr22.pdf> from 
which he derives hit efficiency as a function of distance from the wire. 
This work was previously presented at the Tracking Meeting.

He showed an example track passing through a cell (page 2) which 
demonstrates the variation in drift trajectories. He showed the 
efficiency as a function of DOCA for various track angles (page 3). Here 
there is not much variation in the behavior as a function of angle. The 
main source of inefficiency is that for large drift distances, 
ionization arrives at the wire over an extended time, due to diffusion 
(page 4). That in turn leads to a lower peak pulse height even though 
the integrated charge collected may not be much different from 
ionization that travels a shorter distance. The lower peak pulse height 
may not cross the hit threshold, causing the hit to be lost. One 
consequence is that the efficiency has a strong dependence on the 
applied threshold.

At present, in the simulation this effect is not there. Any reduction in 
efficiency will come only from tracks having a small path inside a cell. 
In simulation, this explains the much sharper drop in efficiency as a 
function of DOCA compared to that seen in Lubomir's result.

Richard pointed out that there is an energy threshold of sorts applied 
in HDGeant4 on energy loss in a cell summed over all particles that 
traverse the cell (multiple tracks from the event, or accidentals), but 
this does not take into account the reduced probability of threshold 
crossing due to large diffusion for long drift distances.

Lubomir's plots show the coefficients of his parametrization of 
efficiency. Richard will take a stab at incorporating the efficiency 
curves into mcsmear.


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