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LHCb Simulation Validation

LHCb Birmingham has an ongoing participation in the development of the experiment's simulation framework, a large part of which involes the validation of new versions of Geant4 physics lists. These are validated independantly of Gauss and as part of the Gauss software.

Geant4 in LHCb

The LHCb Gauss framework uses Geant4 to simulate the passage of particles through matter. The descriptions of particle behaviours are determined by "physics lists" which are compositions of physics models. What model is invoked to describe the behaviour depends on the physical process, particle energy and random number generators for continuity at model boundaries.

Hadronic Physics Lists:

LHEP (Low and High Energy Paramerterisation)

These Physics Lists are based on a parametrised modeling for all hadronic interactions for all particles. The parametrised model is an improved version of the Geisha model. This list combines the high energy parametrised model (HEP) and the low energy one (LEP) describing hadronic interactions. There is a sharp switch from the low to high energy model at 25 GeV? . The modeling of elastic scattering off a nucleus and of capture of negative stopped particles and neutrons proceeds via parametrised models.

FTFP_BERT
  • Bertini cascade (BERT) model, which simulates the intra-nuclear cascade, followed by pre-equilibrium and evaporation phases of the residual nucleus, for protons, neutron, pion and kaons interaction with nuclei at kinetic energies below 9.9 GeV? . The Bertini model produces more secondary neutrons and protons than the LEP model, yielding a better agreement with experiment data.
  • Fritiof (FTF) model for protons, neutrons, pions, kaons interactions with nuclei at high energies. The change between the two models happens with a shaded shift from BERT to FTF that starts at 4 GeV? and ends at 5 GeV? .
QGSP_BERT

Bertini cascade at low energy, switching to LEP at ~9.5GeV and QGSP at 25GeV.

Electromagnetc Physics Lists

The electromagnetic physics list constructors are described on the Geant4 webpage:

http://geant4.web.cern.ch/geant4/collaboration/working_groups/electromagnetic/physlist.shtml

LHCb has a private list "EmLHCb" tailored for use with the experiment, and "EmNoCuts" which is "EmLHCb" without the production cuts.

Documentation of Recent Validation Studies

For the incorporation of Geant4 v9.5 into Gauss, hadronic and electromagnetic validation studies were undertaken. The documented results can be found here:

GaussValidation.pdf 23/05/2013

-- PeterGriffith - 23 May 2013

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