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Pnd4CFitter - how to use it [message #15385]

Fri, 30 August 2013 15:03

Elisabetta Prencipe (2)
Messages: 214
Registered: February 2013

first-grade participant

From: *ikp.kfa-juelich.de

Dear Rho experts,

I am reconstructing the meson Ds(2536)+ through its decay to D*0 K+, D*0 to D0 gamma, D0 to K-pi+.

With the vertex fit or the mass constrained fit, no problems...I mean, I get troubles with the reconstruction of neutrals such as gammas, but this is another topic. My question now is the following: I have my Ds2535 list, and I write:

for (j=0;j<Ds2535.GetLength();++j)
{
Pnd4CFitter fitter(Ds2535[j],ini);
fitter.FitConserveMasses();
double chi2_4c=fitter.GetChi2();
hm_chi2_4c->Fill(chi2_4c);

if (chi2_4c<40)
{
RhoCandidate *jfit = Ds2535[j]->GetFit();
RhoCandidate *jfit2=Ds2535[j]->Daughter(0)->GetFit();

h_4cf->Fill(jfit->M());
h_4cf2->Fill(jfit2->M());

}
}

The histograms are filled, but with crazy results. What am I doing so wrong? thank you for any feedback!
Elisabetta

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Re: Pnd4CFitter - how to use it [message #15386 is a reply to message #15385]

Fri, 30 August 2013 15:40

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: 2.235.190*

The 4-contraints fit forces the final 4-momentum, sum of the decay products, to be exactly like the initial one.

If you have a formation experiment, i.e. pbarp->h_c, then you can use the 4C fitter since you know the p at rest and the projectile pbar, but if you have a reaction like pbarp->DD you cannot use it to force the mass of one single D, since you don't know its initial 4-momentum. You can force the DD state, but not the single D.

I suppose this is ther eason why it does not work in your case.

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Re: Pnd4CFitter - how to use it [message #15388 is a reply to message #15385]

Fri, 30 August 2013 15:45

Klaus Götzen
Messages: 293
Registered: June 2006
Location: GSI

first-grade participant

From: *gsi.de

Hi Elisabetta,

could you try to use the PndKinFitter instead and compare? It works like this:

PndKinFitter fitter(Ds2535[j]);
fitter.Add4MomConstraint(ini);	
fitter.Fit();	
			
double chi2_4c = fitter.GetChi2();
double prob_4c = fitter.GetProb();
			
if ( prob_4c > 0.01 )
{
    RhoCandidate *dstarfit = Ds2535[j]->Daughter(0)->GetFit();
...
}

Best,
Klaus

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