Configuration of Simulation

The G4DarkBreM package follows Geant4's structure of separating particles from processes and specific models of processes from the process itself. This means configuring the package requires three steps.

1. Define the dark photon mass with G4APrime::Initialize
2. Define how the model should behave with g4db::G4DarkBreMModel::G4DarkBreMModel
3. Define which model the process should use with G4DarkBremsstrahlung::G4DarkBremsstrahlung

Besides definition of the dark photon mass, all of the parameters that change how the dark brem physically behaves are defined within the model. The process contains some functionality (for example, limiting the simulation to only one dark brem interaction per event); however, these parameters are second to the model parameters.

It is common to do both of these steps within a G4VPhysicsConstructor since that class can be registered with a Geant4 PhysicsList and handled later by Geant4. An example G4VPhysicsConstructor is provded by g4db::example::APrimePhysics.

Physics Parameters

There are other parameters that tune the functionality of the simulation, but the parameters listed here are directly related to how the physics of the simulation is done.

Parameter	Required	Location	Description
A' Mass	Yes	G4APrime	Mass of dark photon in MeV
A' tau	No	G4APrime	Proper lifetime of dark photon in seconds, only relevant if decay mode is set to GeantDecay (default -1, meaning no decay)
Decay Mode	No	G4APrime	Choice of whether to allow the A' to decay and the decay distribution. The only decay channel is e+/e- (default NoDecay)
MG/ME Data	Yes	g4db::G4DarkBreMModel	Library of dark brem events
Use Muons	Yes	g4db::G4DarkBreMModel	Choice to dark brem off muons or electrons
Minimum DB Threshold	No	g4db::G4DarkBreMModel	Minimum energy in GeV lepton needs to have to DB (default twice A' mass)
Mixing Strength	No	g4db::G4DarkBreMModel	Mixing strength between dark photon and SM photon (default 1.0)
Scaling Method	No	g4db::G4DarkBreMModel	Choice of how to scale the outgoing kinematics from the library (default ForwardOnly)
Xsec Method	No	g4db::G4DarkBreMModel	Choice of WW approximation variant to calculate the total cross section. Options include Full, Improved, HyperImproved, and Auto (default is Auto where Full is used if the A' to lepton mass ratio is below the max and Improved is used otherwise)
Maximum mass ratio	No	g4db::G4DarkBreMModel	If using Auto Xsec Method, the maximum ratio of A' to lepton mass to transition from Full WW to Improved WW (default 50.0)
A' LHE ID	No	g4db::G4DarkBreMModel	If MG/ME Data is in the form of LHE files, the PDG ID of the A' inside of those files (default 622)
Scale A'	No	g4db::G4DarkBreMModel	Whether to scale the outgoing dark photon energy along with the recoil lepton (default false, meaning the dark photon will conserve total momentum while ignoring the nuclear recoil)
Min A' decay distance	No	g4db::G4DarkBreMModel	When A' decay mode is set to FlatDecay, this is the minimum lab-frame distance in mm the A' will travel before decaying (default 0)
Max A' decay distance	No	g4db::G4DarkBreMModel	When A' decay mode is set to FlatDecay, this is the maximum lab-frame distance in mm the A' will travel before decaying (default 1)
Only One per Event	No	G4DarkBremsstrahlung	Limit the dark brem process to only one interaction per event (default false)
Global Bias	No	G4DarkBremsstrahlung	Bias the dark brem process everywhere by this factor (default 1.0)