[Halld-offline] HDGeant4 Meeting Minutes, November 5, 2019

[Mark Ito]

I know that you all have been waiting for this, and here it is 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_November_5,_2019#Minutes> 
as well as below.


    HDGeant4 Meeting, November 5, 2019, Minutes

Present:

  * *CMU: * Naomi Jarvis
  * *FSU: * Sean Dobbs
  * *JLab: * Alex Austregesilo, Mark Ito (chair), Igal Jaegle, Simon
    Taylor, Beni Zihlmann
  * *UConn: * Richard Jones

There is a recording of this meeting <https://bluejeans.com/s/EGhEW/> on 
the BlueJeans site. Use your JLab credentials to get access.


      Announcements

  * Naomi alerted us to a recent Analysis Note from Nilanga
    Wickramaarachchi where he sees a discrepancy between HDG3 and HDG4.
    Alex commented that it amounts to a factor of two difference in
    acceptance for the t-channel and a strange dip in acceptance in the
    u-channel. He will mention this at tomorrow's Production and
    Analysis Meeting. He also noted that Peter Pauli has seen similar
    acceptance differences.
  * Beni announced that he has succeeded building the entire GlueX
    Software stack on Ubuntu 19.04 (Disco). This distribution ships with
    GCC 8.3. He noted a huge spike in memory use when compiling
    DRootGeom.cc from the HDGEOMETRY library. % GB of swap space was
    needed. Richard thought that this might have something to do with
    compiler optimization on a large, script-generated source code file.


      Review of minutes from the last meeting

We went over the minutes from October 22 
<https://halldweb.jlab.org/wiki/index.php/HDGeant4_Meeting,_October_22,_2019#Minutes> 
without significant comment.


      Visualization with OpenGL

Igal has been having trouble running hdgeant4 using OpenGL to do event 
visualization. He gets an error that points to OpenGL libraries and the 
program crashes. He has not seen this problem with Geant4 version 9, 
only version 10.

Richard told us he uses OpenGL often and is committed to maintaining 
this piece of functionality. He will consult with Igal offline.

Richard also mentioned that he uses a package called VirtualGL 
<https://virtualgl.org/About/Introduction> to access local graphics 
acceleration hardware while using a VNC to run Geant4 on a remote node.


      Python Interface Problem

Igal reports an issue using the Python interface to hdgeant4. There 
appears to be a conflict between different versions of the boost 
libraries. Richard cautioned us that hdgeant4 will not work through the 
Python interface if multi-threaded operation is turned on in the build. 
You need a single-threaded build for it to work due to issues with the 
SciPy library. Igal will try that.


      Neutron Simulation

We reviewed Issue #125 
<https://github.com/JeffersonLab/HDGeant4/issues/125>. In light of this 
issue, Igal suggested that we use the "high precision" option in the 
physics list if we want to do neutron propagation with Geant4. We need 
to look into this.


      Segfault from G4VoxelNavigation::ComputeStep

We reviewed Issue #118 
<https://github.com/JeffersonLab/HDGeant4/issues/118>. Naomi will return 
to this when she succeeds in getting a free moment or two.


      Overall BCAL energy shift?

We reviewed Issue #113 
<https://github.com/JeffersonLab/HDGeant4/issues/113>. There is an 
energy shift in the BCAL response when comparing G3 to G4. Richard will 
be taking another look at this one.

Igal suggested looking at the difference without smearing.

Igal also asked about whether the same low-energy cut-offs. Richard 
reminded us that the scheme used in G4 is to stop tracking when particle 
range gets small rather than when particle energy gets small, as is done 
in G3. This makes matching of thresholds between the two systems hard if 
not impossible.


      Difference in Acceptance between G3 and G4

We reviewed Issue #111 
<https://github.com/JeffersonLab/HDGeant4/issues/111>. Colin Gleason 
reported this issue in his analysis. We will go back to him and ask if 
this is still a problem for him. If so, it may need to be repeated with 
modern versions of software.


      Feature request - progress indicator

This is Issue #107 
<https://github.com/JeffersonLab/HDGeant4/issues/107>. Richard is on it.


      Reading in # events and source

Richard estimated that Issue #105 
<https://github.com/JeffersonLab/HDGeant4/issues/105> would take about 
an hour to address.


      Terminal cleanup?

Issue #102 <https://github.com/JeffersonLab/HDGeant4/issues/102> is on 
Richard's list.


      Calorimeter timing mismatch between g3 and g4

We then discussed Issue #93 
<https://github.com/JeffersonLab/HDGeant4/issues/93>, having to do with 
charged particle timing measurements in out two calorimeters. Alex 
wondered if the problem seen here is the same as those reported by Colin 
and Nilanga, i.e, large differences in overall acceptance for a 
particular channel as a whole between G3 and G4.

Mark suggested that calculating efficiency from Monte Carlo could be 
very difficult if accuracy depends on getting the tails of distributions 
correct. We might be better off studying efficiency in data alone. 
Richard thought that that approach might be subject to large systematic 
effects.

Igal suggested that in this case as well, comparisons of the unsmeared 
reconstruction might be informative.

Alex will try to look at single particle responses in data and see how 
they compare to the two Monte Carlos.

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  * This page was last modified on 13 November 2019, at 19:15.

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