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keyword=Empty ref cell runs for 2.1 GeV at 6 degree

Here the yt spectra for the empty ref cell runs taken at 2.1 GeV at 6 degree (fig. 1).
The pink curve is for the elastic kinematics
The yellow one is for kinematics 5.10
The blue one is for kinematics 5.11
The green one is for kinematics 5.12
The black and red ones are for kinematics 5.13 (runs taken at different times)

The first bump at yt=-0.025 is glass or Be scattering making its way around the collimator. From w spectrum, it's heavy so it must be mostly glass.
The second bump at yt=-0.006 is the residual gas and/or the background arising from 2-step process. If one looks at a yt spectrum from a filled ref cell yt, one sees that the acceptance is peaked at the same location (see fig 2.), hence the bump for the empty cell runs.
For the elastic kinematics, there is an additional bump at yt=-0.015. I don't know what this is.
We can see that the yield from the first bump is decreasing with the decreasing momentum, as expected from the cross section. The yield from the residual gas and/or 2 steps process seems to increase slightly with the decreasing momentum (red becomes higher than blue and green. Green becomes similar blue), although this is not sure. If this is true, this would be the signature of a slowly rising 2-step background. But since the rise is small and not clear, this could come simply from the residual gas that have a small random pressure each time we empty the ref cell.
Note that there is no 2-step background for elastic so we don't consider the pink curve.
The upstream collimator is situated at yt=0.0029 and we see no sign of it. That means that the background arising from elastic punching thru the collimator is not visible (yet).

FIGURE 1

FIGURE 2