Another suggestion during the meeting, Wednesday before last, was to evaluate a mass window symmetric about the pion mass. The nominal window has been 0.1 < m_γγ < 0.2 GeV/c². In principle if the backgrounds are properly corrected, the answers should be consistent no matter the window. However, it appears there is some non-negligible change when switching to a mass window of 0.12 < m_γγ < 0.18 GeV/c². One thought was that perhaps a mass window symmetric about the pion mass would be more well-behaved. Here, I plot the various asymmetry calculations for three different mass windows (the nominal, systematic, and an alternative systematic window of 0.105 < m_γγ < 0.165 GeV/c²) on a common axis. These data are, again, the runs currently in Steve's list excluding the BBC-timebin-only events, as decided during the meeting. Following this update, I shall evaulate the asymmetries for an additional set of runs with and without relative luminosity information.

Figure 1: A_N vs. x_F

Plotted are the central values and statistical uncertainties for the various asymmetry extractions with differing mass windows. For bin-1 in x_F > 0, it appears the symmetric mass window does not diverge as much from the nominal window. The same is true in bin-2 for x_F < 0. In other cases, the symmetric window diverges a bit more than the asymmetric window but typically the difference is similar.

Figure 2: A_N vs. p_T

As in Fig. 1, I plot x_F < 0 on the left and x_F > 0 on the right. There appear to be four cases (one being a bin we shall exclude) where the symmetric window diverges from the nominal central values more so than does the asymmetric window. Overall, however, the symmetric window is either closer to the central values or diverges similar to the asymmetric window. From this study I would argue the symmetric mass window is a better option for this analysis, at the very least for a systematics evaulation. Perhaps, at the end of the day, we will decide a symmetric window works better for the central values, as well. However, this is probably a secondary concern to other issues, at the moment.