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Home » PANDA » PandaRoot » Fast Simulations » [FIXED] Problems with PndKinFitter::AddMassConstraint
icon8.gif  [FIXED] Problems with PndKinFitter::AddMassConstraint [message #16518] Mon, 05 May 2014 17:54 Go to previous message
StefanoSpataro is currently offline  StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino
first-grade participant

From: *
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]);

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
    (Size: 12.89KB, Downloaded 759 times)
  • Attachment: jpsi.gif
    (Size: 11.51KB, Downloaded 808 times)
  • Attachment: ana_ste.C
    (Size: 6.94KB, Downloaded 451 times)

[Updated on: Fri, 12 September 2014 10:33]

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