[d2n-analysis-talk] Background sources

[Diana Parno]

Hi all,

Here are the plots Gregg and I were talking about with regard to  
sources of background. These use most of our cuts but there's no E/p  
cut and no preshower threshold cut. These DO cut out the particles  
that passed through the rescattering center. For each x bin, the y  
axis is preshower energy in MeV and the x axis is shower energy in  
MeV. The plot is for negatively charged T2 particles.

If you look at, say, the second x bin (0.2 < x < 0.3, middle of the  
top row) you can see a distribution that's flat at about E_{ps}=100  
MeV. This looks like pions to us, and is easily removed by the  
preshower threshold cut. But when we start getting to higher x (say  
x>0.6), you can see the smear above it that's the same shape as the  
main distribution in 0.2 < x < 0.3. As we move higher and higher in x,  
that sparse distribution stays in the same place while the primary  
distribution moves further and further away. We think that that  
background belongs to events that have been assigned to the wrong x  
bin -- the momentum is erroneously high, but in the calorimeter they  
behave like standard-issue particles at moderate x values. This looks  
like the dominant source of background in high x bins. It's not due to  
the same rescattering that we saw earlier -- those events have already  
been removed from these samples. The clean separation makes them  
simple to remove via an E/p cut, however.


Best,
Diana
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