Minutes of 18 January 2019 Meeting of Geant4 Technical Forum
Editor: A. Morsch, 21 January  2019
- Starting at 16:00

General introduction and prospects
==================================
+ see slides for details
- Next release early December 2019
- Next TF March/April 2019
  - The main topic is the 2019 work plan. The draft will be published in advance. Users are asked to provide feedback.
    Users are encouraged to provide input on requirements.


 

Highlights of version 10.5 - non–physics part
===================================================================
+ see slides for details
- S03 VecGeom is expected to have no impact on the gdml file format. User should provide feedback if there is any.
- S03 VecGeom benchmark: some improvement for complex geometries.
- S04 Looper settings have been always under user control; now available via methods in G4PhysicsListHelper


Highlights of version 10.5 - EM physics part
==================================================================
+ see slides for details

Highlights of version 10.5 - hadronic physics part
==================================================================
+ see slides for details
- Q: What is the recommended physics list for E < 5 MeV ? A: QCS + BIC


Birk's Quenching
==================================================================
+ see slides for details
- For scintillator-based calorimeters, the coefficient used for Birks quenching was obtained from old measurements, by
fitting under the assumption of no delta-ray emissions. Birk's coefficient was underestimated.
- Proposal to to fit the Birks coefficient by imposing the π/e ratio in simulation to be the same as measured
in test-beam data at one beam energy (arbitrarily chosen)
- Si based calorimeter should not have this problem, but it is remarked that there might be other density effects.
- Some concern is expressed that this procedure absorbs all other model systematics. In particular, it is not clear 
how this is related to the fact that the inclusion of more precise physics has led to worse results (slide 2)

Status of open requirements
===========================
+ see slides for details
+ New requirements
- 4701: More realistic matrix element for decays tau->nu+hadrons
- 4702: Inclusion of gamma polarisation effects in high-energy EM models. Difficult but requested by ATLAS and CMS.
- 4703: Improved light nucleon production in FTFP_BERT (to provide similar performance to FTFP_INCLXX)
+ Open requirements 
- 4002 Reweightable uncertainties for systematic uncertainty estimation: in progress and note in preparation
+ Closed
- 4301 Correct pion elastic model for T2K: Cross-sections fixed, no manpower for quasi-elastic channels
- 3901 Complete destruction of G4 objects at exit: done


**** New Requirements

ALICE
=====
+ see slides for details
- Suggestion to consider new default DeltaIntersection parameter which works for all LHC experiments
- Suggestion to print warning messages in case Geant4 finds excessive errors on the bending angle.

ATLAS
=====
+ see slides for details
+ Requests:
  - Allow Geant4 to deal with zero-lifetime particles (needed for quasi-stable particle simulation) 
  - Improving the robustness of commands executed via G4UIManager.
- Some discussions on the speed-up from neutron transport optimisation. Understand overall contribution of neutrons to 
transport time. 

CMS
===
+ see slides 
+ Requests
  - Killed track issue regarded as critical
  - Support from Geant4 to find optimal transport parameters according to user requirements.
    (request similar to ALICE). 
  - For example requirement on relative error on bending angle would translate into specific transport parameters.
 

Modeling Dust Clouds in Geant4
==============================
+ see slides 
+ Ara will contact Makoto on 
  - What are the generic applications of dusty environment modelling capability to the GEANT4 community?
  - What features should we add?
  - What tests should we perform?
- Suggestion to assign precalculated seeds to each voxel for parallel processing.

AOB
Next Geant4 TF in March/April (TBA)