In order to evaluate the
contamination by the Al entrance and exit windows, a run with the Al
frame as a target was done. For this type of analysis, one has to take
the respective thickness of the Al frame and the entrance/exit windows
of the target. One more thing to take care of is the elastic rates in
the detectors as a function of the target position. Indeed, from
simulation made by Jean sebastien real , the rates that we actually see
in the detectors are depending on the Z position of the target that we
consider (Al Frame, entrance window, LH2..).
Figure 1 : Estimation of the contamination by the entrance and exit
window :
The red lines represent the rates for the LH2 target as a function of
fpd's for ced 6.
The blue lines represent the rates fot the Al Frame which are
tranformed ( Preliminary results ) to the scale of of the
entrance and exit windows.
The green lines are an estimation of 10 % of the electron rates that
are lost in the pion rates.
More accurate analysis with
flyswatter and radiator :
Another more accurate way to do it is to take the data with the
flyswatter + radiator, radiator only and Al Frame as the target. In
fact the Z position of the flyswatter is close to the one of the exit
window and the Z position of the Al Frame is close to the one of the
entrance window. So the flyswatter is used to evaluate the
contamination from the exit window and the Al Frame is used to evaluate
the contamination from the entrance window.
The radiator here just mimic the effect of photoproduction ; The
radiator doesnt not only radiate, so we have to substract the rates as
follow :
Rate_(exitWindow) = F x ( Rate_(Fly+Rad) - Rate_(RadOnly) ).
With ' F ' a scaling factor due to the difference of thickness between
the exit window and the radiator.
On the Figure 2 , you can see the most recent results from this
analysis.
Figure 2 : rates in ced 6 :
Red line - LH2 production run
Grey line - Total contribution from the entrance and exit window
derived from Al frame, radiator and flyswatter data.
Pink line - Exit window contribution derived from the flyswatter
and radiator data.
Blue line - Entrance Window contribution derived from the Al frame data.
Asymmetries :
Figure 3 : Al frame elastic asymmetry (old elastic locus
definition)
Figure 4 : C12 elastic asymmetry ( old locus definition )
