Using systematics in NUISANCE

NUISANCE can be linked against various systematics packages, such as GENIE ReWeight, T2K ReWeight, NEUT ReWeight, NOvA ReWeight and the MINERvA tunes, amongst others.

Each systematics packages has a selection of parameters (often referred to as "knobs" or "dials"). For GENIE ReWeight in v2.12.10, these are found in ${GENIE}/src/ReWeight/GSyst.h in the AsString(GSyst_t syst) function. An example is the charged current quasi-elastic axial mass ("MAQE"), encoded as "MaCCQE" in GSyst.h.

Adding systematics is done by providing an additional line in the card file. Taking the example of "MaCCQE" in GENIE ReWeight, NUISANCE needs to know the parameter name, the nominal value to reweight to (which creates the generator prediction), and the type of parameter, e.g. a genie_parameter, a custom_parameter and so on.

Using GENIE ReWeight

Finding the parameters

For GENIE 2 the full list of reweightable parameters is found in genie/src/ReWeight/GSyst.h in GSyst::AsString(GSyst_t syst):

Finding the central values

Finding the 1 sigma uncertainties

Using NEUT ReWeight

Finding the parameters

NEUT ReWeight closely follows GENIE ReWeight by design. For NEUT the list of reweightable parameters is found in neut/src/reweight/NSyst.h. In NEUT 5.3.6 we have