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Measurement of Impact parameter [message #2079] Tue, 05 October 2010 04:51 Go to previous message
Messages: 18
Registered: October 2008
Location: Bristol/RAL

I have been doing some simple simulation and track reconstruction using muons generated by the particle gun to test a vertex geometry that I have built in Mokka. To get a benchmark I used the vxd05 and the vxd03 vertex detectors in the ILD00 geometry. When I plotted the sigma of a fit to the impact parameter residuals I noticed that the D0 impact parameter resolution was worse than the Z0 as a function of momentum (1-10GeV). I then looked at the impact parameter resolution as a function of phi and noticed that at two point in phi I was getting a gaussian like rise in the resolution, which was confirmed when I checked the covariance matrix of D0; this effect is not seen in Z0. The effect occurs in both the vxd05 and vxd03 detectors, but oddly not in my design, although I still see a slightly better Z0 resolution.

The gun direction was set to 89 degrees and was set to step in phi by 1 degree each event and I ran for 10,000 events. I then did another test where I aimed at one of the points in phi where I was seeing this effect and smeared uniformly over it. For the reconstruction I used a marlin steer file based on the LOI steer file.

I am checking the other covariance matrices at the moment and checking the pulls again, both mean and sigma, but if anyone else has any ideas why I am seeing this effect please let me know. I have attached a couple of plots to illustrate.
Also I have checked the other track parameters both LDC and Si and I dont see anything odd as a function of phi.

If you need more information then please let me know.



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