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Extracting flux from gsimple files

gsimple flux files can be used to extract the near detector flux for ND cross-section measurements. These files live in

/pnfs/nova/data/flux/gsimple/

which contains a folder for each new version of nova flux. For reference, the files used in the second analysis used nova_v08 version of the flux files.

The gsimple files contain flux tree, which has three branches. Documentation on the information contained in these branches can be found at $GENIE/src/FluxDrivers/GSimpleNtpFlux.h. The entry branch contains information about the neutrino itself, while the numi branch contains the neutrino parent information.

The entry.vtx variables are the position of the neutrino at the flux window. These variables, and the direction of the momentum variables, are in the near detector coordinate system, but the numbers are in meters, instead of cm. The unit of energy related variables is GeV.

In addition to the flux tree, these files also contain a meta tree, which holds information about the flux window. The leaves of this branch are also documented in GSimpleNtpFlux.h. The neutrino starting position, in x direction for instance, is taken as:

windowBase.x + (random 0:1)*windowDir1.x + (random 0:10)*windowDir2.x