The top plot has the number of "hits" for each mirror. The highlighted mirrors are 6"x6" mirrors on the center rows. The mirrors with the highest counts of those shaded are mirrors #17 and #65, which are the mirrors the beam traverses. This is good, the threshold for protons in Freon-114 is approximately 17 GeV/c. Note that the protons to radiate only 10% of the maximum number of photons at the beam momentum.
The bottom plot shows the up and down mirrors in two bins. If the vessel is partially full, the air and Freon will have separated out, the Freon on the bottom. Recall that the pion threshold in air is 6 GeV/c and for protons, 40 GeV/c. There should be no signal from protons. The pion momentum spectrum is most likely peaked between 250 and 750 MeV/c, and falls rapidly to zero above 1 GeV/c (true for p+p interactions at this energy). There should be few pions with sufficient momentum to radiate in air. While there is an up/down asymmetry, the efficiency/gain differences and "dead channels" have not been factored out. There is a 20% asymmetry here. However, the central two rows show much less asymmetry, and what there is might be explained by the fact that the Cerenkov counter is high with respect to the beam. This might also account for some of the overall asymmetry.
This is a very preliminary analysis on raw data only. I think that we can conclude that there is Freon in the vessel on the basis of this first look. A more detailed analysis will have to be performed using reconstructed tracks incident on the Cerenkov.
More data seems to indicate that the situation changes quickly, and that the definition of "full" based on this analysis is rather rough. This is the current state of the counter:
Last Updated: May 18, 1996