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vertex fitting [message #17255]

Mon, 08 September 2014 13:26

Alexandros
Messages: 51
Registered: January 2014
Location: KVI

continuous participant

From: *kvi-cart.rug.nl

Hi all,

Is there something wrong with the code below??Because I get a segmentation break with these lines and without everything works perfectly..
The problem seems to be in the red line...
Any ideas??

// store the 4-vector of the truth matched candidate (or a dummy, if not matched to keep ntuple consistent)
RhoCandidate *truth = d0[j]->GetMcTruth();
TLorentzVector lv;
if (truth) lv = truth->P4();
qa.qaP4("trd0", lv, nd0);

PndKinVtxFitter *vtxfitter=new PndKinVtxFitter(truth); // instantiate a vertex fitter
vtxfitter->Fit();

RhoCandidate *d0fitvtx = truth->GetFit(); // access the fitted cand
Float_t chi2_vtx = vtxfitter->GetChi2(); // access chi2 of fit
Float_t prob_vtx = vtxfitter->GetProb(); // access probability of fit

TVector3 d0Vtx = d0fitvtx->Pos(); // and the decay vertex position
nd0->Column("vtxprob", (Float_t) prob_vtx);
nd0->Column("vtxchi2", (Float_t) chi2_vtx);
nd0->Column("vtxposx", (Float_t) d0Vtx. Dead

));
nd0->Column("vtxposy", (Float_t) d0Vtx.Y());
nd0->Column("vtxposz", (Float_t) d0Vtx.Z());

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Re: vertex fitting [message #17256 is a reply to message #17255]

Mon, 08 September 2014 14:07

Ralf Kliemt
Messages: 507
Registered: May 2007
Location: GSI, Darmstadt

first-grade participant

From: *gsi.de

Hi Alexandros,

You try to fit a MC-Truth candidate. I have two objections against that: Firstly it does not have a PidCandidate object and not all featureas, esp. Vertexing, are available. Secondly it is the truth and should not be processed by a fitter, because vertex and fourmomenta are true and the truest truth. Smile

Try some reconstructed candidate.

Cheers
Ralf

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Re: vertex fitting [message #17257 is a reply to message #17256]

Mon, 08 September 2014 14:21

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *lnf.infn.it

I suppose a MC truth has no covariance matrix, then it cannot be fitted.

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Re: vertex fitting [message #17263 is a reply to message #17257]

Wed, 10 September 2014 11:38

Alexandros
Messages: 51
Registered: January 2014
Location: KVI

continuous participant

From: *kvi-cart.rug.nl

Hi again,
I have one more question..
I am trying to calculate ctau for D0 meson in my analysis(123micrometers)
From the mc the calculation is correct(125micrometers).
From the vertex information I get 185micrometers..
I have looked several times my code and I could not find a single mistake..
Is there a chance, since we are talking about micrometers that the resolution is not good or there is something else wrong??
I attach my code and my results to get an idea..
Thanks!!

Attachment: Analysis.C
(Size: 12.57KB, Downloaded 314 times)
Attachment: Draw.C
(Size: 3.03KB, Downloaded 296 times)
Attachment: distance_from_IP.pdf
(Size: 17.98KB, Downloaded 344 times)
Attachment: betaVSenergy.pdf
(Size: 34.63KB, Downloaded 285 times)
Attachment: ctau_and_beta*gamma_mc.pdf
(Size: 16.88KB, Downloaded 294 times)
Attachment: ctau_and_beta*gamma_data.pdf
(Size: 17.11KB, Downloaded 293 times)

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Re: vertex fitting [message #17264 is a reply to message #17263]

Wed, 10 September 2014 11:57

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *lnf.infn.it

Why you are not fitting in the whole range?

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Re: vertex fitting [message #17266 is a reply to message #17264]

Wed, 10 September 2014 12:07

Alexandros
Messages: 51
Registered: January 2014
Location: KVI

continuous participant

From: *kvi-cart.rug.nl

It doesn't change anything..
I still have 50-60 micrometers difference Sad

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Re: vertex fitting [message #17267 is a reply to message #17266]

Wed, 10 September 2014 12:08

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *lnf.infn.it

The mine was a question.
However, to be correct, the reco plot should be corrected for efficiency.

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Re: vertex fitting [message #17269 is a reply to message #17267]

Wed, 10 September 2014 12:51

Alexandros
Messages: 51
Registered: January 2014
Location: KVI

continuous participant

From: *kvi-cart.rug.nl

I am sorry I didnt get you..
what do you mean by that??

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Re: vertex fitting [message #17271 is a reply to message #17269]

Wed, 10 September 2014 14:59

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *lnf.infn.it

If you have an efficiency high close to the IP and smaller far, then your fit will be biased. Then, in general, one uses simulation to evaluate the efficiency as a function of the position, and after you use this function to correct your experimental data.
The fact that you have a mean life different from the MC tells you that the reconstruction efficiency is not flat as a function of the distance. But I would not be scared by this.

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Re: vertex fitting [message #17272 is a reply to message #17271]

Wed, 10 September 2014 15:15

Alexandros
Messages: 51
Registered: January 2014
Location: KVI

continuous participant

From: *kvi-cart.rug.nl

ok then, i will try to find a way of doing what you propose..
thanks a lot!!! Very Happy

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