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D0 Secondary Vertex Reconstruction

Updated on Fri, 2010-12-03 16:36. Originally created by rusnak on 2010-11-29 18:36.

 

Data used for the analysis:

10k Hijing Au+Au events, each event contains 5 D0, Branching ratio D0->K-pi+ 100%

 D0 were reconstructed using the Kalman Fitter

 

Cuts

General Cuts:

pTCut          = 0.1;  // transverse momentum cut                                                                                                                             
mKpipiMin      = 1.2;  // min mass of (Kpipi) association                                                                                                                     
mKpipiMax      = 2.2;  // max mass of (Kpipi) association                                                                                                                     
DcaCut         = 0.2;  // single track DCA to PV                                                                                                                              
TpcCut         = 15;   // TPC hits fitted                                                                                                                                     
TrackLengthCut = 40;   // min value for dEdxTrackLength                                                                                                                       
SiCut          = 2;    // (PIX+IST+SSD) hits fitted                                                                                                                           
SigmaPionCut   = 2.5;    // ndEdx for pion                                                                                                                                    
SigmaKaonCut   = 2.5;    // ndEdx for kaon                                                                                                                                    
EtaMin         =-1.0;  // min track pseudorapidity                                                                                                                            
EtaMax         = 1.0;  // max track pseudorapidity                                                                                                                            
zcut           = 10;    // zvertex cut                                                                                                                                        
PrimZResCut    = 0.02; // sigmazvertex cut                                                                                                                                    
sigmaTCut      = 2.0;  // ratio single track dca/sigmaDca                                                                                                                     
ProbKFCut      = 0.01; // probability of fit                                                                                                                                  
refit          = 0;    // flag to refit daughters

charge K = -1, charge pi = +1

 PixK=2 and Pixpi=2 //number of hits in the pixel detectors

Additional Cuts

  • DecayLength/DecayLengthError >
  • DCApi x DCAK < //(only) transversal projection of the DCA of pion * t.p. of the DCA of Kaon
  • cos(theta)> // theta = angle between the D0 momentum vector and join of primary and secondary vertex
  • DCA12 < //closest distance between pi and K track

CUTS OPTIMIZATION

 

4 bins in pT of D0:

  • pT < 0.6 GeV/c
  • 0.6 < pT < 1.0 GeV/c
  • 1.0 < pT < 1.5 GeV/c
  • pT > 1.5 GeV/c 

pT < 0.6 GeV/c

  cos(theta) cut +DCApi x DCAK cut                                                                                             DecayLength/DecayLengthError cut + DCApi x DCAK cut

 

0.6 < pT < 1.0 GeV/c
 cos(theta) cut +DCApi x DCAK cut                                                                                             DecayLength/DecayLengthError cut + DCApi x DCAK cut

 

 1.0 < pT < 1.5 GeV/c  

 cos(theta) cut +DCApi x DCAK cut                                                                                             DecayLength/DecayLengthError cut + DCApi x DCAK cut

Invariant mass spectra of the D0 candidates:

 

the Significance can be slightly increased by appliing additional cut - DCA12:

 
cos(theta) cut + DCA12 cut + DCApi x DCAK cut                                                                     DecayLength/DecayLengthError cut + DCA12 cut + DCApi x DCAK cut 

                 DCApi x DCAK < -1.00 .10-4 cm2                                                                                                      DCApi x DCAK < -1.00 .10-4 cm2 

 

 

                    DCApi x DCAK < -1.0 .10-4 cm2                                                                                                      DCApi x DCAK < -1.0 .10-4 cm2 

 

 

             DCApi x DCAK < -1.1 .10-4 cm2                                                                                                      DCApi x DCAK < -1.1 .10-4 cm2 

 

 

                 DCApi x DCAK < -1.1 .10-4 cm2                                                                                                      DCApi x DCAK < -1.1 .10-4 cm2

 

pT > 1.5 GeV/c 

 cos(theta) cut +DCApi x DCAK cut                                                                                             DecayLength/DecayLengthError cut + DCApi x DCAK cut

Invariant mass spectra of the D0 candidates:

After background subtraction:

Decay Length Error - pT dependence:

             

These high-pT high DLerror candidates are mostly pairs with small value of |phi K- phi pi|:

 

             

 

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