Generators

Generators

The generator files we have are fairly self-explanatory but it doesn't hurt to explain them further. Here, we'll go through gen_gam_tgt line-by-line and outline the possible options.

Physics List

        PhysicsList: QGSP_BERT

This is the Geant4 physics list that will be used by the simulation. Here are a few possible options:

QGSP_BERT
QGSP_BERT_HP
QGSP_BERT_noRadi
QGSP_BERT_HP_noRadi

Note that a default value is set in env.sh under the environment variables PHYSICSLIST.

Particle Type

#General setting
        Type:      simple #(simple/stable/ion)

Particle type can be one of the following options:

simple: ???
stable: ???
ion: ???

Particle Name

        Particle:  gamma #(e+/e-/deuteron/chargedgeantino/gamma/...)

The initial particle can be any of the standard geant4 particles.

Initial Direction

#Default Direction
#                  Theta    Phi
#                  deg      deg
#       Direction: 0        180
#       ThetaSpread:        1.71887
#       PhiSpread:          180

The direction of the beam can be set here, where theta and phi spreads can be defined separately(?)

Initial Momentum

#Default Momentum Amplitude
#                    MeV
#       MomAmp:      0.12178
#       MomAmp:      0.2447
#       MomAmp:      0.34427
#       MomAmp:      0.7789
#       MomAmp:      0.96401
#       MomAmp:      1.08578
        MomAmp:      1.40795

The amplitude of momentum for the initial particle can be defined here. (Can MeV be changed to GeV?)

Initial Position

#Default Position     x    y   z
#                         mm   mm  mm
        Position:         0    0   0
        PosSpread:        100  100 100
#       PosLimit:         17.5

The initial position is defined here, along with a spread. (What's PosLimit?)

Possible Modes

        RandMode:       none #(none/root)
        EnergyMode:     none #(root/histo/none)
#       PositionMode:   bRand #(uniform/root/none/gRand/uRand)
        PositionMode:   target #(uniform/root/none/gRand/uRand/target)
        DirectionMode:  uniform #(none/uniform/histo)
        ThetaMode:      none #(none/gRand/uRand)
        PhiMode:        none #(none/gRand/uRand)
        TimeMode:       none #(none/root)
        pidMode:        none #(none/root)

Several things can be defined in a random mode. The options for each one are given above where:

root: obtained from a root file (?)
histo: obtained from a histogram (how do we let g4sim know which histogram to use?)
uniform: uniformly distributed
gRand: random Gaussian distribution
uRand: random spherical distribution
bRand: random box distribution
target: generate particle inside target (position mode only)

Initial Time

#Default Time
#                ns
        Time:    0

Can set the initial time here