[d2n-analysis-talk] E/p Correction Factors & Effects on Pion Rejection Efficiencies

[David Flay]

Hey Brad,

Regarding:

"The fact that the overall efficiencies are 'lower' for 1.70 GeV (the
cleaner electron sample) than for 0.6 GeV (more pions) bugs me a bit.  I
feel like the explanation should be obvious, but it doesn't quite make
sense to me right now -- I guess I'll have to dig up your definition
of efficiency..."

During Diana's presentation today (which went well I thought!), JP Chen
mentioned something that sheds light on the situation, and is something
that has been in the back of my mind for some time -- he made a comment on
the pion rejection efficiency plot I provided to Diana shown in the talk,
saying that the observed momentum dependence (in the pion rejection
efficiency in the Cerenkov) is not truly a reflection of a drop in the
ability of the Cerenkov to reject pions, but rather shows the poor ability
of the PR to act as a good detector to choose particles (whether they be
electrons or pions).  So, it is in fact an indication of the contamination
level in the original sample itself in the PR.

In which case -- this is clearly demonstrated by the E/p distributions I
sent you last night, where the pion tail leaks into the electron peak. 
Therefore, it's certainly clear that no matter what cuts I impose without
use of the Cerenkov, that obtaining a very clean sample of electrons is
going to be quite difficult (in the PR, at least).  So the question that I
have been thinking of -- is how do I get a clean enough sample of
electrons in the PR to demonstrate the Cerenkov's ability to detect
electrons, given this issue?  There are only so many cuts I may impose,
and use of just the first layer of the PR as a cut is of great help, but
doesn't clear up the contamination to a very high degree as I originally
was hoping.

Dave

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David Flay
Physics Department
Temple University
Philadelphia, PA 19122

office: Barton Hall, BA319
phone: (215) 204-1331

e-mail: flay at jlab.org
      david.flay at temple.edu

website: http://www.jlab.org/~flay
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