Shifting Alignment Parameters in G4LBNF

Beam parameters such as horn currents and positions will not be perfectly known. Limited knowledge of these parameters leads to systematic uncertainty in neutrino flux predictions. These uncertainties are generally assessed by shifting parameters by their tolerances in the beam simulation and comparing the resulting neutrino flux to the unaltered flux. Below is some documentation of how to make various shifts in G4LBNF.

  • Horn Current
    • As of this writing, the horn current is set to 293 kA, with a nominal uncertianty of 3 kA
    • It can be changed in g4lbnf by modifying the line
      /LBNE/det/seHornCurrent <new_horn_current> kA
    • This should be set before the /LBNE/det/construct command
  • Horn and target positions
    • The following shifts horn position from their nominal (on-axis) position by 1-sigma (0.5 mm) in the x direction:
      /LBNE/Surveyor/PosUpstreamLeftBallHorn1 0.5 0.0 0.0
      /LBNE/Surveyor/PosUpstreamRightBallHorn1 0.5 0.0 0.0
      /LBNE/Surveyor/PosDownstreamLeftBallHorn1 0.5 0.0 0.0
      /LBNE/Surveyor/PosDownstreamLeftBallHorn1 0.5 0.0 0.0
      /LBNE/det/TargetAndHorn1RadialSafety 0.1 mm

      Be careful to check the log files for overlaps when moving the targets and horns. It is easy for them to run into each other, which invalidates geant4's results. The target can be moved via: