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Different x-y resolutions [message #12295] Tue, 19 July 2011 13:16 Go to previous message
Simone Bianco is currently offline  Simone Bianco
Messages: 29
Registered: January 2009
continuous participant
From: *cb.uni-bonn.de
Dear Tracking experts,

I am simulating simple events with 4 pions (2pi+ and 2 pi-) with a momentum of 1GeV/c, which are propagated from (0,0,0). I am generating these particles with an homogeneus distribution in phi and in theta (where theta is restricted to the range [20,140]°).
The simulations are performed with all the detectors in, but I set as active only the MVD, the Stt, the GEMs and the forward tracer.
I perform my reconstruction using:
PndMvdRiemannTrackFinderTask,PndSttTrackFinderReal,PndSttMvdTracking,Pnd RecoKalmanTask,PndMCTrackAssociator,PndPidCorrelator (with pion hypothesis),PndPidIdealAssociatorTask.
At the end of this chain I am running some analysis using the PndVtxPoca vertex finder.
I fill histograms with the three components of the reconstructed vertices. As you can see in the attached figures I get a significantly different sigmas for x and y.
index.php?t=getfile&id=6523&private=0
X always looks worse (even with different momenta and theta ranges).
I have already tried with different topologies like using two particles instead of four, or using pions of the same charge, but I always get worse results for X.
I tried with different vertexing tools (POCA, Ralf's fast fitter, another implementation of the POCA) and I always noticed this behaviour. It really seems to come from previous steps since if I try to rotate of 90° the tracks just before running the POCA vertex finder I obtain symmetrical results (worse Y than X, see the second figure attached).
index.php?t=getfile&id=6524&private=0

Does any of you have an idea about possible reasons of this effect?

Thanks in advance.

Cheers,

Simone
 
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