GSI Forum: Analysis » vertex reconstruction without fitting?

Home » PANDA » PandaRoot » Analysis » vertex reconstruction without fitting?

Show: Today's Messages :: Polls :: Message Navigator

vertex reconstruction without fitting? [message #17469]

Fri, 07 November 2014 19:12

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

Report message to a moderator

Re: vertex reconstruction without fitting? [message #17470 is a reply to message #17469]

Fri, 07 November 2014 20:29

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

Report message to a moderator

Re: vertex reconstruction without fitting? [message #17472 is a reply to message #17470]

Sat, 08 November 2014 15:25

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

Report message to a moderator

Re: vertex reconstruction without fitting? [message #17473 is a reply to message #17472]

Sat, 08 November 2014 15:41

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

Report message to a moderator

Re: vertex reconstruction without fitting? [message #17474 is a reply to message #17473]

Sat, 08 November 2014 16:40

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?

Report message to a moderator

Re: vertex reconstruction without fitting? [message #17475 is a reply to message #17474]

Sat, 08 November 2014 16:44

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.

Report message to a moderator

Re: vertex reconstruction without fitting? [message #17476 is a reply to message #17474]

Sat, 08 November 2014 16:46

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

Report message to a moderator

Re: vertex reconstruction without fitting? [message #17477 is a reply to message #17476]

Sat, 08 November 2014 17:02

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

Report message to a moderator