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icon5.gif  Vertex fitters' problems [message #14847] Thu, 06 June 2013 12:40 Go to previous message
StefanoSpataro is currently offline  StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino
first-grade participant

From: *
Dear all,
Laura and me are checking the features of our vertex fitters,
with the trunk version 20077. In the latest trunk the function GetMcTruth() returns null pointer, than the trunk cannot be used.

We have simulated 10k ppbar->D*+D*-->D0pi+D0barpi-->k-pi+pi+k+pi-pi-, we have used MC truth index to identify the kaon- and the pion+ of the D0 (we have not touched the d0bar).
We have uploaded all the relevant macros, you have only to modify the path of the DEC file in the sim macro.

We run PndKinVtxFitter, PndVtxPoca and PndVtxPRG and compared the results. We were able to find a tutorial only for PndKinVtxFitter. The tutorial for PndVtxPoca and PndVtxPRG is missing then we hope we are using them in the proper way.

Please check the code.

Vertex residuals reco - mc (in cm) and chi2 for PndKinVtxFitter:


Vertex residuals reco - mc (in cm) and chi2 for PndVtxPoca:


Vertex residuals reco - mc (in cm) and chi2 for PndVtxPRG:


These are the obtained resultion values:

                |X res  | Y res | Z res                |
PndKinVtxFitter |   2um |   2um | wrong and asymmetric |
PndVtxPoca      | 400um | 400um | 400um                |
PndVtxPRG       |  60um |  60um | 100um                |


PndKinVtxFitter is obtaining very very very narrow distributions on X and Y. How is it possible? Z distribution is screwed. Chi2 is very low.
PndVtxPoca has too large resolution values, does not work. Decent chi2 maybe.
PndVtxPRG has more reasonable values, even if I believe they are a bit large. It is much slower than the others, most probably because of the 10 iterations, but w/o a tutorial we were not sure about which number to use. Chi2 too low.

Still not checked composite particles (i.e. D*)


What to use? Could you please take a look?

Many tanks in advance.

Laura and Stefano
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