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PndKinFitter Mass constraints and resolution [message #15745]

Fri, 22 November 2013 12:16

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *to.infn.it

I was checking what is stored by the ana_complete.C macro, and I was taking a look into the jpsi invariant mass after the fitter (PndKinFitter) putting a mass constraint.
Checking the hjpsim_mcf histo, at a first glance the mass peak seems a delta as I would expect, but just increasing the binning and zooming I realized that it has a distribution and a width of 5 MeV. Now the question is: why it is not a delta? If I constraint that the mass is a specific value, I should expect such value, and not a distribution (at least this is what I was finding when running kinematic fitters for hades). It is not
clear to me why there is such behavior, I have received such a question.
Is it possible that the fitter finds local maxima and not the good one? Or maybe it stops after X iterations even if it has not find the set value? Or maybe there is some bug?

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