Following from NuMI note 1321-v1 by the Texas boys work has gone into G4NuMI to better model the Hadron Absorber.

First plots showing the bi-modal distribution of the charge deposition in Muon Monitor 1.
Fig. 1

The 2D histogram shows that Muon Monitor one is pretty well centered in the middle of the beam. Bob Zwaska also gave me coordinates such that the positioning was not done ad hoc. The important bit anyway is that the monitor is horizontally positioned in the middle of the beam, because the theory is that the muons causing the bi-nodal shape are slipping through the gaps between the Absorber Core and the surrounding shielding, approximately a gap of <1inch. Bin size is 40mm.
Fig. 2

The following is with a bin size of 20mm

What we get from the plots:

• Histogram of x-pos shows a shift towards -x, similar to data
• also similar to the data is that shape is similar as well, two nodes, with the larger on the -x side
  
• The y-pos histogram shows the greatest effect of the gap effect because there's only one node and that's at +y, which makes sense because there are no gaps between the bottom of the absorber and the shielding... just the top

The data for muon monitor 1 is for charge deposition which is flat with muon energy above a certain threshold. G4Numi is not constrained by only charge deposition information but establishes the energy of the muons as they 'swim' through the various bits of the MC. The following is a Histogram of the muon momentum as it crosses muon monitor 1. Bin size 20mm.
Fig. 3
 
The money plot though ends up being the moment/hits to get a look and see if the shape is not flat.
Fig. 4

It is now very easy to see that the portion of the muons slipping through the cracks are affecting the data in muon monitor 1. Just like the data as well this effect gets smeared out in Muon Monitors 2 and 3.