[Halld-offline] HDGeant4 Meeting Minutes, March 9, 2021

[Mark Ito]

Folks,

Please find the minutes here 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_March_9,_2021#Minutes> 
and below.

   -- Mark

     __________________________________________


    HDGeant4 Meeting, March 9, 2021, Minutes

Present: Tegan Beattie, Mark Ito (chair), Richard Jones, Zisis 
Papandreou, Churamani Paudel, Lubomir Pentchev, Justin Stevens, Simon 
Taylor, Nilanga Wickramaarachchi

There is a recording of this meeting 
<https://bluejeans.com/s/wKdTln_kEz3/> on the BlueJeans site. Log into 
the BlueJeans site first to gain access (use your JLab credentials).


      Review of minutes from the last meeting

We went over the minutes from February 23rd 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_February_23,_2021#Minutes>. 
Richard has already made the proposed changes to the 
tagger-hit-to-energy conversion 
<https://mailman.jlab.org/pipermail/halld-offline/2021-February/008475.html>. 
Pull requests await merging in the halld_recon and halld_sim repositories.


      New wiki page: Particle Gun Collection

Richard described an upcoming historical catalog of single particle gun 
simulations. See his new wiki page 
<https://halldweb.jlab.org/wiki/index.php/Particle_Gun_Collection> for 
the complete description.


      Issues on GitHub

We went over the issues <https://github.com/JeffersonLab/HDGeant4/issues>.


        Hits in both CALs from the same track

Lubomir led us through a discussion of Issues on GitHub 
<https://github.com/JeffersonLab/HDGeant4/issues/185>. Two ideas that 
came up:

  * There might be an effect where a charged particle's trajectory is
    extrapolated beyond what is reasonable, allowing it to hit the FCAL
    and create a spurious match there.
  * Particles that clip the corner of the BCAL and send parts of the
    shower into the FCAL could explain some of the double matching. This
    behavior could be different between G3 and G4.

For all the details, see the Issue itself, linked above.


        Proton timing in the BCAL

Again, Issue #179 <https://github.com/JeffersonLab/HDGeant4/issues/179> 
has mainly to do with late hits in the BCAL from charged hadrons. Tegan 
presented results from a study to determine the physical mechanism for 
the late hits, as usual,comparing the effects among G4, G3/HADR1, and 
G3/HADR4. It turns out identifying parent particles for the particles 
creating late hits was not possible in an unambiguous manner. He was 
able to plot the timing distributions for the various physical 
interaction mechanisms separately, again comparing the different Geant 
engines. In fact, some of these interactions happen quite late, tens of 
nanoseconds after the event.

For all of the details see Tegan's plots on the DocDB 
<https://halldweb.jlab.org/doc-private/DocDB/ShowDocument?docid=4878>. 
They are the ones with "MAR04" in the name.


        G3/G4 Difference in FDC wire efficiency at the cell boundary

Richard reported on the root cause of Issue #181 
<https://github.com/JeffersonLab/HDGeant4/issues/181>. Interestingly, 
the G3 simulation agrees better with the data because of the requirement 
that only one cell in a layer is hit. This artificially eliminates hits 
from tracks that spend a small amount of time in a cell, but happily 
since those trajectory have lower detection efficiency, their 
elimination mimics what is seen in data. The G4 simulation has no such 
mechanism for eliminating corner-clipping tracks and so hits with long 
drift times are produced at a rate higher than seen in the data.

See the Issue, linked above, for a more detailed explanation, with 
diagrams.

We seemed to be forming a consensus that Richard should allow multiple 
hits per layer, but implement an efficiency function that reduced the 
number of large DOCA hits.

[Added in press: in the issue itself you will see Richard's description 
of adding actual wires to the FDC simulation geometry.]


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.jlab.org/pipermail/halld-offline/attachments/20210315/40e050b0/attachment.html>