Goal:

Properly model the signal and background to the invariant mass plots using four single particle MC sets normalized to fit the data.  Further, subtract out background contributions to arrive at a raw yield for each pt bin.

Details:

Data Vs. Single Particle MC (see here)

Cuts:

• Data events pass L2gamma trigger and L2gamma software trigger
• Cand Pt > 5.5
• Charged Track Veto
• At least one good strip in each SMD plane
• Z Vertex found and |vtx| < 60.
• Zgg < .7

Bins:

9 pt bins, with boundries {5.5, 6., 6.5, 7., 7.75., 9., 11.5, 13.5, 16., 21.}

Plots:

 1)

Above is a plot of the invariant mass distributions for the 9 pt bins used in this analysis.  The black crosses represent the data (with errors.)  The four colored histograms show the invariant mass distributions of pion candidates found in single pion MC (purple), Single photon MC (red), single eta MC (blue) and mixed-event MC (green).  The four distributions are simultaneously fit to the data.  

 2)

The above plot shows a data/MC comparison, where the red MC curve is the sum of the four single particle curves shown in plot 1.  As you can see (especially in bins 3-7) the single particle MC seems to be underestimating the width of the pion peak, especially on the high mass side.  The MC peak is too narrow.  I think this can be explained by two effects.  First, I am overestimating the energy precision of the towers and SMDs.  The width of the mass peak is directly related to the energy resolution of the towers and SMD.  I think this is telling us that the simulated resolution is too precise.  Also, there is the issue of jet background, which is not present in these simulations and would tend to add small amounts of energy to each photon (thus increasing the mass and the pt of the pion candidate.)

Conclusions:

Obviously this MC parameterization is not quite good enough to compare to the data.  I want to go back and remake the MC distributions with more smearing in the energy resolution, and perhaps with a small pt-dependent term to simulate the jet background.