Geant4 neutrino interaction processes
Geant4 neutrino processes include three flavour oscillation, neutrino-electron and neutrino-nucleus interactions. The interactions are available in both charged and neutral current modes.
The user neutrino process management is located in the
G4NeutrinoPhysicsMessenger
class (in the domain
/physics_lists/nu/
). The messenger is in connection with the
G4NeutrinoPhysics
constructor that is included in the majority of
Geant4 physics lists. Neutrino activation and tuning have to be chosen
before the /run/initialize
command.
Neutrino oscillation process
In the user macro file:
/physics_lists/factory/addNeutrino # adds G4NeutrinoPhysics on the top of PL
/physics_lists/nu/NuOscDistanceName rBaseLine # oscillation L name
/physics_lists/nu/NuOscDistanceBias 5.0e4 # L is biased
...
/run/initialize
...
The first command activates the neutrino physics. It is mandatory for all neutrino processes. Then the user defines the oscillation distance G4Region name and the reduction length bias (\(10^3\) km is not suitable for the Geant4 geometry, 1000 km/50000=20 m).
Neutrino-electron process
The G4NeutrinoElectronProcess
class with biased charge and
neutral current cross-sections in a detector G4Region:
/physics_lists/factory/addNeutrino
/physics_lists/nu/NuEleCcBias 1.0 # charged current is not biased
/physics_lists/nu/NuEleNcBias 5.0e14 # neutral current is biased
/physics_lists/nu/NuDetectorName lTarget # detector region name
...
/run/initialize
...
The process gets the cross-sections
(G4NeutrinoElectronNc(Cc)Xsc
) as well as charge and neutral
current final state models (G4NeutrinoElectronNc(Cc)Model
).
Here the neutral current cross-section is biased only.
Neutrino-nucleus process
User commands:
/physics_lists/factory/addNeutrino
/physics_lists/nu/NeETotXscActivation true
/physics_lists/nu/NuDetectorName gTarget # G4Region name
/physics_lists/nu/NuNucleusBias 1.e12
...
/run/initialize
...
The \(\nu A\) total cross-sections (class
G4MuNeutrinoNucleusTotXsc
) will be biased
(\(\cdot 10^{12}\)) in the G4Region
named gTarget
.
The process G4MuNeutrinoNucleusProcess
manages charge and
neutral current models implemented in classes
G4NuMuNucleusCc(Nc)Model
with x and \(Q^2\)
distributions stored in G4PARTICLEXSDATA->/neutrino/nu_mu
data
set. The biasing has to provide \(\lesssim\) 0.1 neutrino detection
with approximately flat distribution,
(\(1-\exp[-\sigma_{bias}n_{at}L]\sim\sigma_{bias}n_{at}L\)).
Example
All neutrino processes are activated and biased:
/physics_lists/factory/addNeutrino
/physics_lists/nu/NuOscDistanceName rBaseLine # oscillation L name
/physics_lists/nu/NuOscDistanceBias 5.0e4 # L is biased
...
/physics_lists/nu/NuEleCcBias 1.0 # charged current is not biased
/physics_lists/nu/NuEleNcBias 5.0e14 # neutral current is biased
/physics_lists/nu/NuDetectorName lTarget # detector region name
...
/physics_lists/nu/NeETotXscActivation true
/physics_lists/nu/NuNucleusBias 1.e12
...
/run/initialize
...
Another way to add neutrino physics is to add it in the main test program:
G4VModularPhysicsList* phys = nullptr;
...
// define neutrino physics
phys->AddPhysics( new G4NeutrinoPhysics() );
runManager->SetUserInitialization(phys);
...
More details can be found in [Gri19, Gri23] (however they
refer to the old interface via /em/
rather than /nu/
).
Bibliography
- Gri19
V.M. Grichine. Geant4 neutrino-electron interaction model. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 942:162403, October 2019. URL: http://dx.doi.org/10.1016/j.nima.2019.162403, doi:10.1016/j.nima.2019.162403.
- Gri23
V.M. Grichine. Geant4model for neutrino nucleon/nucleus integral cross sections. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1053:168394, August 2023. URL: http://dx.doi.org/10.1016/j.nima.2023.168394, doi:10.1016/j.nima.2023.168394.