FVTX x-vertex scan

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What happens to the resolution if the vertex is not at (0,0,0)?
Using the libraries of 1 Sep 08, and the standard eval macros: 

Files:
runpisa_smooth            throwing a smooth Pisa distribution
event.par                 parameter xyz0_input is varied
Fun4Muons_Pisa.C
Fun4Muons_RecoDST_sim.C
mc_eval_plots.C           for making eval plots
1000 events for each case.

bigger-->   


As the event vertex moves away from 0,0,0, the resolution in R is not much affected up to x=2mm, then it rises.

The matching efficiency is unaffected.


As the event vertex moves away from 0,0,0, the resolution in phi seems to worsen steadily between 0 and 1mm, and then stay the same after that.
In order to understand the patterns seen, I ran some events such that tracks lie along the vertex displacement direction (x), and perpendicular to it.

For the r-resolution, when tracks are in the same plane as the displacement, there is a slight improvement (red), and when tracks are perpendicular, ta slight worsening (green) of the resolution.

This is for phi. The red case is when the vertex offset (along x) lines up with the tracks' phi (~180°). For the other two cases, there is no such fortuitous alignment, and phi resolutions are ~550μm.


Last update 7 Oct 08

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