GSI Forum
GSI Helmholtzzentrum für Schwerionenforschung

Home » PANDA » PandaRoot » Analysis » vertex reconstruction without fitting?
vertex reconstruction without fitting? [message #17469] Fri, 07 November 2014 19:12 Go to next message
AnnaSkachkova is currently offline  AnnaSkachkova
Messages: 9
Registered: April 2013
Location: Dubna
occasional visitor
From: *dubna.ru
Dear colleagues,

could anybody tell me - is it possible in PandaRoot to determine the production vertexes of the final particles (for example electrons and muons in the future) without the reconstruction of the full tree chain of their parents? It is needed for the background study when we do not care about the parents of the final particles, but just of their characteristics.
Could you please give the example of such a code?

Thank you in advance,
Anna
Re: vertex reconstruction without fitting? [message #17470 is a reply to message #17469] Fri, 07 November 2014 20:29 Go to previous messageGo to next message
Ralf Kliemt is currently offline  Ralf Kliemt
Messages: 507
Registered: May 2007
Location: GSI, Darmstadt
first-grade participant

From: *pool.mediaWays.net
Hello Anna,

This is quite straightforward and nothing special. You need to crreate a composite candidate with your part of the charged (!) final state particles. Then feed it to the fitter or POCA calculator, just as you "always do".

		theAnalysis->FillList(muplus,  "MuonAllPlus");
		theAnalysis->FillList(muminus, "MuonAllMinus");
		
		// *** combinatorics for J/psi -> mu+ mu-
		jpsi.Combine(muplus, muminus);
		
		// ***
		// *** do VERTEX FIT (J/psi)
		// ***
		for (j=0;j<jpsi.GetLength();++j) 
		{
			PndKinVtxFitter vtxfitter(jpsi[j]);	// instantiate a vertex fitter
			if( ! vtxfitter.Fit(); ) continue;
			
			double chi2_vtx = vtxfitter.GetChi2();	// access chi2 of fit
			double prob_vtx = vtxfitter.GetProb();	// access probability of fit
			RhoCandidate *jfit = jpsi[j]->GetFit();	// access the fitted cand
			TVector3 jVtx=jfit->Pos();		// and the decay vertex position
		}


Cheers
Ralf
Re: vertex reconstruction without fitting? [message #17472 is a reply to message #17470] Sat, 08 November 2014 15:25 Go to previous messageGo to next message
AnnaSkachkova is currently offline  AnnaSkachkova
Messages: 9
Registered: April 2013
Location: Dubna
occasional visitor
From: *dubna.ru
Thank you, Ralf, for the unswer. But the case when you can combine the particles is understandable and was already described. I wonder about the case when I have for example 2 separate muons in the final state, one coming from kaon, the other is from pion decays. And I want to get their production vertexes (supposing they are different and I do not know their origin). What shall I do? To do the "combinatorics" for a single particle?
Cheers, Anna
Re: vertex reconstruction without fitting? [message #17473 is a reply to message #17472] Sat, 08 November 2014 15:41 Go to previous messageGo to next message
Klaus Götzen is currently offline  Klaus Götzen
Messages: 293
Registered: June 2006
Location: GSI
first-grade participant
From: *adsl.alicedsl.de
Hi Anna,


you can access the MC truth origin of a reco particle by something like

  fAnalysis->FillList(muons, "MuonAll");
  ...
  RhoCandidate *truth = muons[i]->GetMcTruth();

  if (truth!=0)
  {
    TVector3 trueOrigin = truth->Pos();
    ...
  }

if this is what you meant.


Best,
Klaus
Re: vertex reconstruction without fitting? [message #17474 is a reply to message #17473] Sat, 08 November 2014 16:40 Go to previous messageGo to next message
AnnaSkachkova is currently offline  AnnaSkachkova
Messages: 9
Registered: April 2013
Location: Dubna
occasional visitor
From: *dubna.ru
Yes, Klaus, thank you. I meant the reconstructed vertex of any particle without accotiation of this particle with any other one. And the coordinate in this case will be, for example Vx = muons[i]->Pos().Dead); right? Is it in mm?
Re: vertex reconstruction without fitting? [message #17475 is a reply to message #17474] Sat, 08 November 2014 16:44 Go to previous messageGo to next message
StefanoSpataro is currently offline  StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino
first-grade participant

From: *ip71.fastwebnet.it
You can reconstruct vertex ONLY if you have two particles. With only 1 particle, you can have the MC vertex but you cannot reconstruct any vertex.
Our standard unit system foresees cm as distances unit.
Re: vertex reconstruction without fitting? [message #17476 is a reply to message #17474] Sat, 08 November 2014 16:46 Go to previous messageGo to next message
Klaus Götzen is currently offline  Klaus Götzen
Messages: 293
Registered: June 2006
Location: GSI
first-grade participant
From: *adsl.alicedsl.de
Hi Anna,


just to make it clear: a single track (=charged particle) cannot have a reconstructed vertex (or origin), since tracking only determins the trajectory (helix) of a charged particle, but not the starting point of the track on that helix. A vertex information can only be assigned by combining it with at least a second track and the constraint, that both particles originate from the same point.

If you want to know the POCA to the IP of the reco track, you can also use

muons[i]->Pos();


As Stefano wrote (I was just typing when he answered Wink), unit is cm.

Best,
Klaus
Re: vertex reconstruction without fitting? [message #17477 is a reply to message #17476] Sat, 08 November 2014 17:02 Go to previous messageGo to next message
AnnaSkachkova is currently offline  AnnaSkachkova
Messages: 9
Registered: April 2013
Location: Dubna
occasional visitor
From: *dubna.ru
Thank you everybody who unswered! So, I understand that if I have the only single charged particle, or I do not know with which other charged particle it can be accotiated (the neutral ones cann't be combined, right?) I can have only MC approximation, described as Klaus wrote (for x coordinate): Vx = muons[i]->Pos().Dead). Right?
Anna
Re: vertex reconstruction without fitting? [message #17478 is a reply to message #17477] Sat, 08 November 2014 17:06 Go to previous messageGo to next message
Klaus Götzen is currently offline  Klaus Götzen
Messages: 293
Registered: June 2006
Location: GSI
first-grade participant
From: *adsl.alicedsl.de
Precisely: The point-of-closest-approach (doesn't have to be close to the true origin) to the IP of the reco track is

muons[i]->Pos;

The MC-truth origin is given by

muons[i]->GetMcTruth()->Pos();

(in case the pointers aren't NULL)

Re: vertex reconstruction without fitting? [message #17479 is a reply to message #17478] Sat, 08 November 2014 17:08 Go to previous message
AnnaSkachkova is currently offline  AnnaSkachkova
Messages: 9
Registered: April 2013
Location: Dubna
occasional visitor
From: *dubna.ru
Ok. Thank you all once again.

Best regards, Anna
Previous Topic: PndVtxPRG vs PndKinVtxFitter
Next Topic: Different results for same information extracted in different ways
Goto Forum:
  


Current Time: Thu Jan 27 10:23:13 CET 2022

Total time taken to generate the page: 0.01009 seconds