Home » PANDA » PandaRoot » Fast Simulations » [FIXED] Problems with PndKinFitter::AddMassConstraint
[FIXED] Problems with PndKinFitter::AddMassConstraint [message #16518] 
Mon, 05 May 2014 17:54 
StefanoSpataro
Messages: 2736 Registered: June 2005 Location: Torino

firstgrade participant 
From: *to.infn.it


Dear all,
most probably the "analysis" topic would be better, but since I did the tests with fast sim then I report here.
I run the standard psi(2S) > J/psi pi+ pi which you can find in macro/scrut simulation macros. I modified the analysis macro (ana_ste.C) in order to have montecarlo ID and to plot some variables from the fit. The analysis macro is attached.
If I take my J/psi pi+pi combinations (psi) and put a 4 constraint fit:
PndKinFitter kinfit(psi2s[j]);
kinfit.Add4MomConstraint(ini);
kinfit.Fit();
I have decent results:
You can see the original invariant mass, the fitted invariant mass (RMS from 48 MeV to 50 KeV), chi2 peaked around 3 (4 degrees of freedom), flat probability between 0 and 1.
But if I try to apply a mass constraint fit to only the mu+mu (J/psi):
PndKinFitter mfitter(jpsi[j]); // instantiate the PndKinFitter in psi(2S)
mfitter.AddMassConstraint(m0_jpsi); // add the mass constraint
mfitter.Fit(); // do fit
Then the results are not so fine:
Invariant mass before and after the fit (RMS from 46 MeV top 6 MeV, which is a big value considering that it is a mass constraint fit and it should be a delta, 1 NDF), chi2 peaked at very low values, and prob not flat.
I would say tht the AddMassConstraint function has some problems.

Attachment: psi.gif
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Attachment: ana_ste.C
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[Updated on: Fri, 12 September 2014 10:33] Report message to a moderator














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