Some generators do not support combined beams or targets. The JOINT input type allows NUISANCE to combined different beam files at run time producing a composite input. NOTE: Inputs from different generators cannot currently be merged, you cannot mix a NEUT and GENIE MC file into a single JOINT input.
How it works
For each entry in a given list of input files NUISANCE will temporarily create an InputHandler and use it to extract the total rate, flux, and number of entries.
A TChain is then formed for the provided generator type and each input is added into the list. NUISANCE keeps track of how many entries were in each TTree and uses this to calculate a separate scaling factor for each set of events. When a JOINT input is being used this scale factor is assigned as the FitEvent.InputWeight value to allow it to be propagated to the event predictions.
To get the best results and ensure that the statistical error on each sample is correct we suggest that the number of events in each sample is proportional to the relative flux integral of each component. For example if generating 1 million events with a numu + numubar flux with integrals of 150 and 500 respectively (arbritrary norm), then the number of events in each sample should be numu=230,769 and numubar=769,230.
Reading JOINT GENIE MINERvA fhc
To read in multiple files and create a joint input file, pass them as a comma seperated list of files enclosed in brackets.
In this example both a FHC numu and FHC numubar event sample will be added together to create a prediction for the MiniBooNE CCQELike data.
sample MiniBooNE_CCQELike_XSec_1DQ2_nu GENIE:(/data/events/genie/minerva/genie_minerva_fhc_numu.root,/data/events/genie/minerva/genie_minerva_fhc_numubar.root)
It is also possible to add different event modes together. For example say you have generated events in GENIE with the Default model, and you would like to add MEC events too. You could read them in as
sample MiniBooNE_CCQE_XSec_1DQ2_nu GENIE:(/data/events/genie/minerva/genie_minerva_fhc_numu_default.root,/data/events/genie/minerva/genie_minerva_fhc_numu_mec.root)
WARNING : When reading in joint inputs the maximum number of events defined by the configuration option "MAXEVENTS" must be set to "-1" otherwise NUISANCE will try and run over the first portion of the event file, and will skip out events in the second input file, completely messing up the relative contribution from each event file.
In NUISANCE v2r0 there is a check for this, but on older versions there is not. You have been warned!