[d2n-analysis-talk] Dilution Factors

[Gregg B. Franklin]

Matt,
   The plots you have are very interesting.  The dilution factor at low 
x is a much bigger effect than we were anticipating.  I think we should 
first try to make sure we agree on the dilution factor determined by the 
reverse polarity run at 4.7 GeV.  It would be useful to plot 1-D instead 
of D since D gets close to 1.0 through much of our range.  Lets make 
sure we agree on the runs, the cuts, etc.

We also want to check the asymmetry, also.  If it is large, this is a 
big problem in addition to just "dilution factor".  We need to at least 
put a bound on the asymmetry.

   For the 5-pass data, the following strategy might work if we have 
enough statistics.

1) Start with the 4.7 GeV data and determine the positrons (from reverse 
polarity running) normalize by charge as a 2-D function of momentum and 
scattering angle.  Call this 2D histogram 1.  It will have to be course 
binned.

2) Do the same for positrons determined from the negative (normal 
polarity) running at 4.7G.   In both cases, we should have mostly just 
positrons.   Call this histogram 2.

3) Determine the ratio of Hisogram 2) over Histogram 1) bin by bin 
should give use the relative acceptance for positrons as a function of 
scattering angle and momentum.  (Our statistics will be poor at high x, 
but hopefully the positrons aren't a problem there.)

3) For the 5-pass data, make hisogram 3 with similar bins for positrons. 
  This will be for the normal polarity, which means the acceptance will 
be very different than for the real data.  However, you can use the 
ratios (bin by bin) determined in step 3 to correct for this.  The 
problem might be that the "4-pass" data may have low statistics in 
kinematics bins that become important at 5-pass.

In the longer run, we can try to understand this ratio with Monte Carlo. 
  If there is a large asymmetry and therefore can depend on the target 
polarization direction, it will be harder.

Regards,
Gregg



-- 
Prof. Gregg B Franklin
Head, Department of Physics
Carnegie Mellon University
phone: (412) 268-2743   fax: (412) 681-0648