The output of GMINOS are fz_gaf files that contain information about "hits". Note in this context a hits is merely information that a certain paricle deposited a certain amount of energy in a certain place in the detector. In general this is not very useful, as it does not tell you how much charge is desposited on a PMT channel. The next step is to convert the fz_gaf file into a reroot file. This reroot file is merely a root-compatible version hit information in the fz_gaf file. Don't be confused by the .root at the end of the name. This file does not contain reconstructed events.
Now you are all set to run the events through loon. In loon there are few things that you must do to the events. First you must convert the hit information (which again just tells you about energy deposition) into photons and you must figure out how many photons actaully strike the PMTs. This is done in the PhotonTransport module. Then the photons must be digitzed and the readout of the detector electronics is simulated in DetSim. Then you can finally reconstruct the events with your favorite reconstruction package. See the User's Manual for more info on running the offline software. For an example of how to configure a loon jobs to run on an MC file, you could look at the batch group's web pages , where you will find links to the actual job scripts used to reconstruct MC files in the official batch processing.
For the gory details, you really should see gminos_jobs.
But to summarize, to generate beam MC events, the first step is to obtain the neutrino beam flux files. These are paw ntuples, that are produced by GNuMI. These are presently stored in AFS space at /afs/fnal.gov/files/data/minos/d87/gnumi. For the far detector is is fairly straightforward to simulate single neutrino interactions. For the near detector the situation is more complicated. The near detector typically has dozens of neutrino interactions per beam spill inside the detector, and there are also numerous CC interactions of muon neutrinos in the rock that produce muons. If these muons are high enough in energy they can enter the near detector through the front face or the sides. So, for the near detector, one first should generate single detector events. (That may be sufficient for your purposes.) You can also generate files of just rock events. The rock events take a really long time to run, since a large area of rock must be considered. Typcially in MC production we generate a smaller sample of rock-only events and reuse them.
The final step is to overlay the single detector events and the signle rock events into snarls (or spills). This is done using a program call reco_minos. During that process, detector events and rock events are randomly distributed over an 8.9 microsecond time window and are reassmbled into one record. Just as is the case with the data, it is then up to the reconstruction software (such as the slicer or the chopper) to try to separate the snarl hits into individual neutrino events. The other complication about the overlay process is that the user must tell reco_minos how many detector events and rock events (on average) to put into each snarl. In order to have some know these numbers to a high degree of accuracy, the user must first generate a large sample of detector events and rock events. (As is described in the gminos_jobs documentation, these numbers can be found by examining the log files.)
|1||Stauts code 3=incoming particle (neutrino in our case) , 1= final state particle|
|2||Particle Code (in the PDG standard format)|
|3||Line # of first mother particle in the event, relative to event start (0 for initial entries)|
|4||Line # of second mother particle in the event, relative to event start (0 if there is only one mother)|
|5||Line # of first daughter particle in the event, relative to event start (0 if it hasn't decayed)|
|6||Line # of final daughter particle in the event, relative to event start (0 if it hasn't decayed)|
|7||x momentum (in GeV/c)|
|8||y momentum (in GeV/c)|
|9||z momentum (in GeV/c)|
|10||energy in GeV|
|11||mass in GeV/c**2|
|12||initial x position, in mm|
|13||initial y position, in mm|
|14||initial z position, in mm|
|15||production time, in mm/c|