While I am waiting for my simulation jobs to finish, I am switching gears for a moment and looking at real data.  I am trying to finalize the mass window I use for my asymmetry measurement.  One of the unknown uncertainties in this calculation comes from the significant low mass background in my pion-candidate mass distribution.  So I am studying this background to try and see how much it will affect my asymmetry when I use different mass windows.  I am basing my treatment of this background on Frank Simon's similar study for the 2005 data (which can be found here.)  Basically the idea is that we simulate a reconstructed pion by taking a single photon and splitting it into two clusters.  This split photon wil reconstruct at a much lower mass.  I then normalize the resulting mass distribution to my real data.  The results from my first pass can be found below.  Each 2x2 plot is one of my Pt bins (with one plot for each spinbit.)  The red histogram is my background model and the black is real 2006 data. 

 




Using the above histograms I have estimated the 'contamination' from the low mass background.  That is, I have calculated what percentage of the pion mas peak might actually be coming from the low mass background.  for the first two bins, if I use a mass window of .08 to .25 (which is what I use for my asymmetry calculation) I have no more than 10% contamination.  For the third and fourth Pt bins, if I use a mass window of .1 to .25 (again, which is what I use for these two bins for my asym calc) I again get no more than 10% contamination.  Next I am planning on using these low mass peaks to estimate the asymmetry (if any) coming from the low mass background.