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[FIXED] Problem with PndVertexFitter for particles with neutral charge [message #18279]

Fri, 29 May 2015 10:44

Jennifer Pütz
Messages: 47
Registered: April 2015
Location: FZ Juelich

continuous participant

From: *ikp.kfa-juelich.de

Hi everyone,

I have a problem with the PndKinVtxFitter. I simulated 1000 events for the reaction pbar p → Xi- Xi+ → lambda0 pi- anti-lambda pi+. The lambda0 decays into a proton and pi- and the anti-lambda0 decays into an anti-proton and a pi+.

If I combine the proton and the pi- to the lambda0 the vertex fitter is working fine. Same for the antilambda0. But when I combine lambda0 and pi- to Xi- the vertex fitter does not work.

To check, if I made a mistake, I went back to an easier reaction: pbar p → Lambda0 AntiLambda0 → proton pi- anti-proton pi+
The vertex fitter is working fine for combining proton and pi- to lambda0. But if I combine lambda0 and anti-lambda0 to the pbar p system, here again the vertex fitter does not work.

index.php?t=getfile&id=8414&private=0

I checked the 4-Mom-Constraint Fitter and it is working.

index.php?t=getfile&id=8413&private=0

Is there already a solution for this problem?

I'm using on my system:

Fairsoft Version: March 15
FairRoot: Master
PandaRoot: Trunk Rev. 27718

Best
Jenny

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Attachment: VertexFit_chi2.png
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Attachment: 4CFit_prob.png
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[Updated on: Wed, 03 February 2016 23:38] by Moderator

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18280 is a reply to message #18279]

Fri, 29 May 2015 11:20

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *to.infn.it

Can you write the piece of code where you are doing such vertex fitting?

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18281 is a reply to message #18280]

Fri, 29 May 2015 11:24

Jennifer Pütz
Messages: 47
Registered: April 2015
Location: FZ Juelich

continuous participant

From: *ikp.kfa-juelich.de

Hi Stefano,

for the vertex fit I'm using:

//*** Cross check: pbar + p -> Lambda0 + AntiLambda0

crossCheck.Combine(lambda0, antiLambda0);
crossCheck.SetType(88888);

for (int j=0; j<crossCheck.GetLength(); ++j){

//do vertex fit
PndKinVtxFitter vertexFitter_cc (crossCheck[j]);
vertexFitter_cc.Fit();
RhoCandidate * ccFit = crossCheck[j]->GetFit();

}

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18282 is a reply to message #18281]

Fri, 29 May 2015 11:26

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *to.infn.it

lambda0 and antiLambda0?

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18283 is a reply to message #18279]

Fri, 29 May 2015 11:37

Jennifer Pütz
Messages: 47
Registered: April 2015
Location: FZ Juelich

continuous participant

From: *ikp.kfa-juelich.de

Ok, sorry I should have give you some more information Embarassed

----

theAnalysis->FillList(piminus, "PionAllMinus", "PidAlgoIdealCharged");
theAnalysis->FillList(piplus, "PionAllPlus", "PidAlgoIdealCharged");
theAnalysis->FillList(proton, "ProtonAllPlus", "PidAlgoIdealCharged");
theAnalysis->FillList(antiProton, "ProtonAllMinus", "PidAlgoIdealCharged");

//***Lambda0 -> PiMinus + Proton
lambda0.Combine(piminus,proton);
lambda0.SetType(3122);

//***AntiLambda0 -> PiPlus + AntiProton
antiLambda0.Combine(piplus,antiProton);
antiLambda0.SetType(-3122);

//*** Cross check: pbar + p -> Lambda0 + AntiLambda0

crossCheck.Combine(lambda0, antiLambda0);
crossCheck.SetType(88888);

for (int j=0; j<crossCheck.GetLength(); ++j){

//do vertex fit
PndKinVtxFitter vertexFitter_cc (crossCheck[j]);
vertexFitter_cc.Fit();
RhoCandidate * ccFit = crossCheck[j]->GetFit();

}

[Updated on: Fri, 29 May 2015 11:37]

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18284 is a reply to message #18283]

Fri, 29 May 2015 11:41

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *to.infn.it

Don't you have to first vertex fit the lambdas, before giving them into the global fitter?

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18285 is a reply to message #18279]

Fri, 29 May 2015 11:47

Jennifer Pütz
Messages: 47
Registered: April 2015
Location: FZ Juelich

continuous participant

From: *ikp.kfa-juelich.de

I do first vertex fit lambdas. I just leave it out here.

---

for (int j=0; j<lambda0.GetLength(); ++j){
PndKinVtxFitter vertexfitterLambda0 (lambda0[j]);
vertexfitterLambda0.Fit();
RhoCandidate * lambda0Fit = lambda0[j]->GetFit();
}

for (int j=0; j<antiLambda0.GetLength(); ++j){
PndKinVtxFitter vertexfitterAntiLambda0 (antiLambda0[j]);
vertexfitterAntiLambda0.Fit();
RhoCandidate * antiLambda0Fit = antiLambda0[j]->GetFit();
}

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18286 is a reply to message #18285]

Fri, 29 May 2015 11:57

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *to.infn.it

In this case maybe you should fit lambda0Fit and not lambda0. Just trying to guess, Klaus and Ralf are the experts.

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18287 is a reply to message #18279]

Fri, 29 May 2015 12:56

André Zambanini
Messages: 17
Registered: February 2012
Location: FZ Jülich

occasional visitor

From: *ext.kfa-juelich.de

I actually have the same problem with a non-working vertex fitter combining a (anti-)lambda with some other particle. If I remember well, Dariusch saw the same.

Other than Jenny, I'm using the particle candidate after the vertex fitting as you just suggested. So my guess is that this is not the issue.

[Updated on: Fri, 29 May 2015 13:02]

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Re: Problem with PndVertexFitter for particles with neutral charge [message #18289 is a reply to message #18279]

Fri, 29 May 2015 14:27

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

first-grade participant

From: *gsi.de

Hi,

The vertex fitters (PndKinVtxFitter/PndKalmanVtxFitter) operate on a minimum of two charged tracks. For anything else you may use PndVtxPoca, which analytically calculates the vertex. From the top of my head:

PndVtxPoca pocafinder;
for (int j=0; j<lambda0.GetLength(); ++j)
{
  PndKinVtxFitter vertexfitterLambda0 (lambda0[j]);
  vertexfitterLambda0.Fit();
  RhoCandidate * lambda0Fit = lambda0[j]->GetFit();
  for (int j=0; j<antiLambda0.GetLength(); ++j)
  {
    PndKinVtxFitter vertexfitterAntiLambda0 (antiLambda0[j]);
    vertexfitterAntiLambda0.Fit();
    RhoCandidate * antiLambda0Fit = antiLambda0[j]->GetFit();
    
    TVector3 pbarpvertex;
    crossCheck.Combine(lambda0Fit, antiLambda0Fit);
    crossCheck.SetType(88888);

    double doca = pocafinderGetPocaVtx(pbarpvertex,crossCheck);
    // now you have a vertex written to pbarpvertex and a measure of the distances between the trajectories (i.e. a quality criterium)
  }
}

If you have charged(!) particles combining to crossCheck, you may want to update the four-momentum along the helix to the vertex via the analysis:

bool check = theAnalysis->PropagateToPoint(crossCheck, pbarpvertex);

Cheers
Ralf

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