[d2n-analysis-talk] inelastic events and misc. events in BigBite

[posik at jlab.org]

Hi all,

   Last meeting Gregg had suggested that I take a look the ratio of
inelastic events to a particular set of low energy high momentum events in
the BigBite.

The first thing I wanted to do was see where the low energy-high momentum
events were falling in the shower/pre-shower. To do this, I first plotted
the total energy vs momentum and selected the low energy-high momentum
events as those that fall within the red box in the plot Neg_EvsP_0.png.

I then plotted the pre-shower(blue) and shower(red) projected track
locations in the plot misc_events_psshlocation.png. In this plot, the
positive vertical track values correspond to events near the bottom of the
physical BigBite shower, and positive horizontal track values correspond
to small angle (beam) side. So we see that most of these low energy high
momentum events are hitting the upper small angle side of the shower.

In order to form a ratio of inelastic events to those low energy high
momentum events, which I will now refer to as misc. events, I altered the
event ID cut a bit. The plot Neg_EvsP.png shows again the energy vs
momentum. In Blue are the inelastic event selection, and in red are the
misc. event selection. These event distributions were chosen as such, so
that the region (low energy low momentum ) where the inelastic events
merge with the misc events was avoided. This was done by requiring the
inelastic events to have an energy > 1200 MeV, and the misc events having
an energy < 1200 MeV and E/p < 0.7. I should mention that all of our
4.7GeV production cuts were applied (can be found on the wiki,
https://hallaweb.jlab.org/wiki/index.php/Analysis_Tools), with the
exception of energy cuts described above and the misc. events, which do
not have the production E/p cut applied because the E/p cut would cut them
out.

I then computed the ratio of inelastic to misc events for 4 runs, and then
computed the weighted ratio over the 4 runs. I ended up with the ratio of

inelastic/misc events =  3.932 +/- 0.065 %

Finally, I also took a look at how the misc. events compare to the
inelastic events in the BigBite Cerenkov ADCs. This can be seen in the
plot Neg_Ration_CerADC.pdf, where I plotted the inelastic events in red
and misc events in blue for several ADCs. On the left are ADCs
4(top),5(middle) and 6(bottom). On the right are ADCs 14(top), 15(middle)
and 16(bottom). Looking at the Cerenkov ADCs, we can see that the misc
events fall right around the mean value of the inelastic events.

-Matt
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