This obviously needs some explaining: the colors corresponding to the nofixedparam are full fits (i.e., gaussian peak for pion, exponential background with a curvature term in it and a gaussian to fit the eta meson peak). Nofixedparam04 corresponds to the full fit with a starting fit range of 0.04 (and ending of 0.8). 06 would be a starting fit range of 0.06 (again, to 0.8). The noeta04,06,08 are the same except the fit function does not include the eta meson peak. Noeta046,066,086 are again fits without the eta meson peak, but begin at 0.04 and end at 0.6 (instead of 0.8), 0.06-0.6 and 0.08-0.6.

The purpose of this plot is to demonstrate how stable the fit is, even though the centroid may be off somewhat due to the W trigger (peak being pushed further up as you get higher in PT).

Note these are for three different PT bins: the first 2-10, second 10-13 and third 13-17 GeV.