X-Git-Url: http://git.uio.no/git/?p=u%2Fmrichter%2FAliRoot.git;a=blobdiff_plain;f=ITS%2FAliITSVertexerZ.cxx;h=0529842f732559add5d83f587997d2da91515912;hp=574b247c705d146c55bfc9f87c418e0d184d6548;hb=eb4ccbd18d14a349144739ade74cf30010dc0ab5;hpb=0c6af5c97bcd3a8de76b097696d4c93083759822

diff --git a/ITS/AliITSVertexerZ.cxx b/ITS/AliITSVertexerZ.cxx
index 574b247c705..0529842f732 100644
--- a/ITS/AliITSVertexerZ.cxx
+++ b/ITS/AliITSVertexerZ.cxx
@@ -12,19 +12,17 @@
  * about the suitability of this software for any purpose. It is          *
  * provided "as is" without express or implied warranty.                  *
  **************************************************************************/
-#include <AliITSVertexerZ.h>
-#include <Riostream.h>
-#include <TString.h>
-#include <AliITS.h>
-#include "AliITSLoader.h"
-#include <AliRun.h>
+#include "AliITSVertexerZ.h"
 #include<TBranch.h>
 #include<TClonesArray.h>
 #include<TH1.h>
-#include<TMath.h>
+#include <TString.h>
 #include<TTree.h>
-#include <AliITSgeom.h>
-#include <AliITSRecPoint.h>
+#include "AliESDVertex.h"
+#include "AliITSgeomTGeo.h"
+#include "AliITSRecPoint.h"
+#include "AliITSRecPointContainer.h"
+#include "AliITSZPoint.h"
 
 /////////////////////////////////////////////////////////////////
 // this class implements a fast method to determine
@@ -34,282 +32,395 @@
 // It can be used successfully with Pb-Pb collisions
 ////////////////////////////////////////////////////////////////
 
+using std::endl;
+using std::cout;
 ClassImp(AliITSVertexerZ)
 
 
 
 //______________________________________________________________________
-AliITSVertexerZ::AliITSVertexerZ():AliITSVertexer() {
+AliITSVertexerZ::AliITSVertexerZ():AliITSVertexer(),
+fFirstL1(0),
+fLastL1(0),
+fFirstL2(0),
+fLastL2(0),
+fDiffPhiMax(0),
+fZFound(0),
+fZsig(0.),
+fZCombc(0),
+fLowLim(0.),
+fHighLim(0.),
+fStepCoarse(0),
+fTolerance(0.),
+fMaxIter(0),
+fWindowWidth(0),
+fSearchForPileup(kTRUE)
+{
   // Default constructor
-  SetDiffPhiMax(0);
-  fX0 = 0.;
-  fY0 = 0.;
-  SetFirstLayerModules(0);
-  SetSecondLayerModules(0);
-  fZFound = 0;
-  fZsig = 0.;
-  fITS = 0;
-  fZCombc = 0;
-  fZCombf = 0;
-  SetLowLimit(0.);
-  SetHighLimit(0.);
-  SetBinWidthCoarse(0.);
-  SetBinWidthFine(0.);
-  SetTolerance(0.);
+  SetDiffPhiMax();
+  SetFirstLayerModules();
+  SetSecondLayerModules();
+  SetLowLimit();
+  SetHighLimit();
+  SetBinWidthCoarse();
+  SetTolerance();
+  SetPPsetting();
+  ConfigIterations();
+  SetWindowWidth();
 }
 
 //______________________________________________________________________
-AliITSVertexerZ::AliITSVertexerZ(TString fn, Float_t x0, Float_t y0):AliITSVertexer(fn) {
+AliITSVertexerZ::AliITSVertexerZ(Float_t x0, Float_t y0):AliITSVertexer(),
+fFirstL1(0),
+fLastL1(0),
+fFirstL2(0),
+fLastL2(0),
+fDiffPhiMax(0),
+fZFound(0),
+fZsig(0.),
+fZCombc(0),
+fLowLim(0.),
+fHighLim(0.),
+fStepCoarse(0),
+fTolerance(0.),
+fMaxIter(0),
+fWindowWidth(0),
+fSearchForPileup(kTRUE)
+{
   // Standard Constructor
   SetDiffPhiMax();
-  fX0 = x0;
-  fY0 = y0;
   SetFirstLayerModules();
   SetSecondLayerModules();
-  fZFound = 0;
-  fZsig = 0.;
-  fITS = 0;
-  fZCombc = 0;
-  fZCombf = 0;
   SetLowLimit();
   SetHighLimit();
   SetBinWidthCoarse();
-  SetBinWidthFine();
   SetTolerance();
+  SetPPsetting();
+  ConfigIterations();
+  SetWindowWidth();
+  SetVtxStart((Double_t)x0,(Double_t)y0,0.);
 
 }
 
 //______________________________________________________________________
-AliITSVertexerZ::AliITSVertexerZ(const AliITSVertexerZ &vtxr) : AliITSVertexer(vtxr) {
-  // Copy constructor
-  // Copies are not allowed. The method is protected to avoid misuse.
-  Error("AliITSVertexerZ","Copy constructor not allowed\n");
+AliITSVertexerZ::~AliITSVertexerZ() {
+  // Destructor
+  delete fZCombc;
 }
 
 //______________________________________________________________________
-AliITSVertexerZ& AliITSVertexerZ::operator=(const AliITSVertexerZ& /* vtxr */){
-  // Assignment operator
-  // Assignment is not allowed. The method is protected to avoid misuse.
-  Error("= operator","Assignment operator not allowed\n");
-  return *this;
+void AliITSVertexerZ::ConfigIterations(Int_t noiter,Float_t *ptr){
+  // configure the iterative procedure to gain efficiency for
+  // pp events with very low multiplicity
+  Float_t defaults[5]={0.02,0.05,0.1,0.2,0.3};
+  fMaxIter=noiter;
+  if(noiter>5){
+    Error("ConfigIterations","Maximum number of iterations is 5\n");
+    fMaxIter=5;
+  }
+  for(Int_t j=0;j<5;j++)fPhiDiffIter[j]=defaults[j];
+  if(ptr)for(Int_t j=0;j<fMaxIter;j++)fPhiDiffIter[j]=ptr[j];
 }
 
-
 //______________________________________________________________________
-AliITSVertexerZ::~AliITSVertexerZ() {
-  // Default Destructor
-  fITS = 0;
-  if(fZCombc)delete fZCombc;
-  if(fZCombf)delete fZCombf;
-}
+Int_t AliITSVertexerZ::GetPeakRegion(TH1F*h, Int_t &binmin, Int_t &binmax){
+  // Finds a region around a peak in the Z histogram
+  // Case of 2 peaks is treated 
+  Int_t imax=h->GetNbinsX();
+  Float_t maxval=0;
+  Int_t bi1=h->GetMaximumBin();
+  Int_t bi2=0;
+  for(Int_t i=imax;i>=1;i--){
+    if(h->GetBinContent(i)>maxval){
+      maxval=h->GetBinContent(i);
+      bi2=i;
+    }
+  }
+  Int_t npeaks=0;
 
+  if(bi1==bi2){
+    binmin=bi1-3;
+    binmax=bi1+3;
+    npeaks=1;
+  }else{
+    TH1F *copy = new TH1F(*h);
+    copy->SetBinContent(bi1,0.);
+    copy->SetBinContent(bi2,0.);
+    Int_t l1=TMath::Max(bi1-3,1);
+    Int_t l2=TMath::Min(bi1+3,h->GetNbinsX());
+    Float_t cont1=copy->Integral(l1,l2);
+    Int_t ll1=TMath::Max(bi2-3,1);
+    Int_t ll2=TMath::Min(bi2+3,h->GetNbinsX());
+    Float_t cont2=copy->Integral(ll1,ll2);
+    if(cont1>cont2){
+      binmin=l1;
+      binmax=l2;
+      npeaks=1;
+    }
+    if(cont2>cont1){
+      binmin=ll1;
+      binmax=ll2;
+      npeaks=1;
+    }
+    if(cont1==cont2){
+      binmin=l1;
+      binmax=ll2;
+      if(bi2-bi1==1) npeaks=1;
+      else npeaks=2;
+    }  
+    delete copy;
+  }    
+  return npeaks;
+}
 //______________________________________________________________________
-AliITSVertex* AliITSVertexerZ::FindVertexForCurrentEvent(Int_t evnumber){
-  // Defines the AliITSVertex for the current event
-
-  fCurrentVertex = 0;
-  AliRunLoader *rl =AliRunLoader::GetRunLoader();
-  AliITSLoader* itsLoader =  (AliITSLoader*) rl->GetLoader("ITSLoader");
-  itsLoader->ReloadRecPoints();
-
-  rl->GetEvent(evnumber);
-
-  if(!fITS)  {
-    fITS = (AliITS*)gAlice->GetModule("ITS");
-    if(!fITS) {
-      Error("FindVertexForCurrentEvent","AliITS object was not found");
-      return fCurrentVertex;
+AliESDVertex* AliITSVertexerZ::FindVertexForCurrentEvent(TTree *itsClusterTree){
+  // Defines the AliESDVertex for the current event
+  VertexZFinder(itsClusterTree);
+  Int_t ntrackl=0;
+  for(Int_t iteraz=0;iteraz<fMaxIter;iteraz++){
+    if(fCurrentVertex) ntrackl=fCurrentVertex->GetNContributors();
+    if(!fCurrentVertex || ntrackl==0 || ntrackl==-1){
+      Float_t diffPhiMaxOrig=fDiffPhiMax;
+      fDiffPhiMax=GetPhiMaxIter(iteraz);
+      VertexZFinder(itsClusterTree);
+      fDiffPhiMax=diffPhiMaxOrig;
     }
   }
+  if(fComputeMultiplicity) FindMultiplicity(itsClusterTree);
+  return fCurrentVertex;
+}  
 
-  fITS->SetTreeAddress();
-
-  AliITSgeom *geom = fITS->GetITSgeom();
-
-  TTree *tR = itsLoader->TreeR();
+//______________________________________________________________________
+void AliITSVertexerZ::VertexZFinder(TTree *itsClusterTree){
+  // Defines the AliESDVertex for the current event
+  fCurrentVertex = 0;
+  Double_t startPos[3]={GetNominalPos()[0],GetNominalPos()[1],GetNominalPos()[2]};
+  Double_t startCov[6]={GetNominalCov()[0],GetNominalCov()[1],GetNominalCov()[2],
+			GetNominalCov()[3],GetNominalCov()[4],GetNominalCov()[5]};
+  ResetVertex();
   TClonesArray *itsRec  = 0;
-  Float_t lc[3]; for(Int_t ii=0; ii<3; ii++) lc[ii]=0.;
-  Float_t gc[3]; for(Int_t ii=0; ii<3; ii++) gc[ii]=0.;
-  Float_t lc2[3]; for(Int_t ii=0; ii<3; ii++) lc2[ii]=0.;
-  Float_t gc2[3]; for(Int_t ii=0; ii<3; ii++) gc2[ii]=0.;
-
-  itsRec  = fITS->RecPoints();
-  TBranch *branch = tR->GetBranch("ITSRecPoints");
-
-  Int_t nbinfine = static_cast<Int_t>((fHighLim-fLowLim)/fStepFine);
-  Int_t nbincoarse = static_cast<Int_t>((fHighLim-fLowLim)/fStepCoarse);
-  if(fZCombc)delete fZCombc;
-  fZCombc = new TH1F("fZCombc","Z",nbincoarse,fLowLim,fLowLim+nbincoarse*fStepCoarse);
-  if(fZCombf)delete fZCombf;
-  fZCombf = new TH1F("fZCombf","Z",nbinfine,fLowLim,fLowLim+nbinfine*fStepFine);
+  // lc1 and gc1 are local and global coordinates for layer 1
+  Float_t gc1[3]={0.,0.,0.}; // ; for(Int_t ii=0; ii<3; ii++) gc1[ii]=0.;
+  // lc2 and gc2 are local and global coordinates for layer 2
+  Float_t gc2[3]={0.,0.,0.}; //; for(Int_t ii=0; ii<3; ii++) gc2[ii]=0.;
+  AliITSRecPointContainer* rpcont=AliITSRecPointContainer::Instance();
+  rpcont->FetchClusters(0,itsClusterTree);
+  if(!rpcont->IsSPDActive()){
+    AliWarning("Null pointer for RecPoints branch, vertex not calculated");
+    ResetHistograms();
+    fCurrentVertex = new AliESDVertex(startPos,startCov,99999.,-2);
+    return;
+  }
 
   Int_t nrpL1 = 0;
   Int_t nrpL2 = 0;
-  for(Int_t module= fFirstL1; module<=fLastL1;module++){
-    if(module%4==0 || module%4==3)continue;
-    branch->GetEvent(module);
-    nrpL1+= itsRec->GetEntries();
-    fITS->ResetRecPoints();
-  }
-  for(Int_t module= fFirstL2; module<=fLastL2;module++){
-    branch->GetEvent(module);
-    nrpL2+= itsRec->GetEntries();
-    fITS->ResetRecPoints();
-  }
-  cout<<"nrpL1 = "<<nrpL1<<"; nrpL2= "<<nrpL2<<endl;
+  nrpL1=rpcont->GetNClustersInLayerFast(1);
+  nrpL2=rpcont->GetNClustersInLayerFast(2);
+
   if(nrpL1 == 0 || nrpL2 == 0){
-    cout<<"achi, achi\n";
+    AliDebug(1,Form("No RecPoints in at least one SPD layer (%d %d)",nrpL1,nrpL2));
     ResetHistograms();
-    return fCurrentVertex;
+    fCurrentVertex = new AliESDVertex(startPos,startCov,99999.,-2);
+    return;
   }
-  Float_t *xc1 = new Float_t [nrpL1];
-  Float_t *yc1 = new Float_t [nrpL1];
-  Float_t *zc1 = new Float_t [nrpL1];
-  Float_t *phi1 = new Float_t [nrpL1];
-  Float_t *xc2 = new Float_t [nrpL2];
-  Float_t *yc2 = new Float_t [nrpL2];
-  Float_t *zc2 = new Float_t [nrpL2];
-  Float_t *phi2 = new Float_t [nrpL2];
-  Int_t ind = 0;
-  for(Int_t module= fFirstL1; module<=fLastL1;module++){
-    if(module%4==0 || module%4==3)continue;
-    branch->GetEvent(module);
-    Int_t nrecp1 = itsRec->GetEntries();
-    for(Int_t j=0;j<nrecp1;j++){
-      AliITSRecPoint *recp = (AliITSRecPoint*)itsRec->At(j);
-      lc[0]=recp->GetX();
-      lc[2]=recp->GetZ();
-      geom->LtoG(module,lc,gc);
-      gc[0]-=fX0;
-      gc[1]-=fY0;
-      xc1[ind]=gc[0];
-      yc1[ind]=gc[1];
-      zc1[ind]=gc[2];
-      phi1[ind] = TMath::ATan2(gc[1],gc[0]);
-      if(phi1[ind]<0)phi1[ind]=2*TMath::Pi()+phi1[ind];
-      ind++;
-    }
-    fITS->ResetRecPoints();
-  }
-  ind = 0;
-  for(Int_t module= fFirstL2; module<=fLastL2;module++){
-    branch->GetEvent(module);
-    Int_t nrecp2 = itsRec->GetEntries();
-    for(Int_t j=0;j<nrecp2;j++){
-      AliITSRecPoint *recp = (AliITSRecPoint*)itsRec->At(j);
-      lc[0]=recp->GetX();
-      lc[2]=recp->GetZ();
-      geom->LtoG(module,lc,gc);
-      gc[0]-=fX0;
-      gc[1]-=fY0;
-      xc2[ind]=gc[0];
-      yc2[ind]=gc[1];
-      zc2[ind]=gc[2];
-      phi2[ind] = TMath::ATan2(gc[1],gc[0]);
-      if(phi2[ind]<0)phi2[ind]=2*TMath::Pi()+phi2[ind];
-      ind++;
+  // Force a coarse bin size of 200 microns if the number of clusters on layer 2
+  // is low
+  if(nrpL2<fPPsetting[0])SetBinWidthCoarse(fPPsetting[1]);
+  // By default nbincoarse=(10+10)/0.01=2000
+  Int_t nbincoarse = static_cast<Int_t>((fHighLim-fLowLim)/fStepCoarse);
+  if(fZCombc)delete fZCombc;
+  fZCombc = new TH1F("fZCombc","Z",nbincoarse,fLowLim,fLowLim+nbincoarse*fStepCoarse);
+
+ /* Test the ffect of mutiple scatternig on error. Negligible
+  // Multiple scattering
+  Float_t beta=1.,pmed=0.875; //pmed=875 MeV (for tracks with dphi<0.01 rad)
+  Float_t beta2=beta*beta;
+  Float_t p2=pmed*pmed;
+  Float_t rBP=3; //Beam Pipe radius = 3cm
+  Float_t dBP=0.08/35.3; // 800 um of Be
+  Float_t dL1=0.01; //approx. 1% of radiation length  
+  Float_t theta2BP=14.1*14.1/(beta2*p2*1e6)*TMath::Abs(dBP);
+  Float_t theta2L1=14.1*14.1/(beta2*p2*1e6)*TMath::Abs(dL1);
+*/
+  Int_t nEntriesMod[kNSPDMod];
+  TClonesArray* recpArr[kNSPDMod];
+  for(Int_t modul=0; modul<kNSPDMod; ++modul) {
+    if(!fUseModule[modul]) {
+      nEntriesMod[modul]=0;
+      recpArr[modul]=0;
+    } else {
+      recpArr[modul]=rpcont->UncheckedGetClusters(modul);
+      nEntriesMod[modul]=recpArr[modul]->GetEntriesFast();
     }
-    fITS->ResetRecPoints();
   }
-  for(Int_t i=0;i<nrpL1;i++){
-    Float_t r1=TMath::Sqrt(xc1[i]*xc1[i]+yc1[i]*yc1[i]);
-    for(Int_t j=0;j<nrpL2;j++){
-      Float_t diff = TMath::Abs(phi2[j]-phi1[i]);
-      if(diff>TMath::Pi())diff=2.*TMath::Pi()-diff;
-      if(diff<fDiffPhiMax){
-	Float_t r2=TMath::Sqrt(xc2[j]*xc2[j]+yc2[j]*yc2[j]);
-	Float_t zr0=(r2*zc1[i]-r1*zc2[j])/(r2-r1);
-	fZCombf->Fill(zr0);
-	fZCombc->Fill(zr0);
+      
+  Int_t maxdim=TMath::Min(nrpL1*nrpL2,50000);  // temporary; to limit the size in PbPb
+  static TClonesArray points("AliITSZPoint",maxdim);
+  Int_t nopoints =0;
+  for(Int_t modul1= fFirstL1; modul1<=fLastL1;modul1++){   // Loop on modules of layer 1
+    if(!fUseModule[modul1]) continue;
+    UShort_t ladder=int(modul1/4)+1;  // ladders are numbered starting from 1
+    TClonesArray *prpl1=recpArr[modul1]; //rpcont->UncheckedGetClusters(modul1);
+    Int_t nrecp1 = nEntriesMod[modul1]; //prpl1->GetEntries();
+    for(Int_t j1=0;j1<nrecp1;j1++){
+      AliITSRecPoint *recp1 = (AliITSRecPoint*)prpl1->At(j1);
+      recp1->GetGlobalXYZ(gc1);
+      gc1[0]-=GetNominalPos()[0]; // Possible beam offset in the bending plane
+      gc1[1]-=GetNominalPos()[1]; //   "               "
+      Float_t phi1 = TMath::ATan2(gc1[1],gc1[0]);
+      if(phi1<0)phi1+=TMath::TwoPi();
+      for(Int_t ladl2=0 ; ladl2<fLadOnLay2*2+1;ladl2++){
+	for(Int_t k=0;k<4;k++){
+ 	  Int_t ladmod=fLadders[ladder-1]+ladl2;
+	  if(ladmod>AliITSgeomTGeo::GetNLadders(2)) ladmod=ladmod-AliITSgeomTGeo::GetNLadders(2);
+	  Int_t modul2=AliITSgeomTGeo::GetModuleIndex(2,ladmod,k+1);
+	  if(modul2<0)continue;
+	  if(!fUseModule[modul2]) continue;
+	  itsRec=recpArr[modul2]; // rpcont->UncheckedGetClusters(modul2);
+	  Int_t nrecp2 = nEntriesMod[modul2]; // itsRec->GetEntries();
+	  for(Int_t j2=0;j2<nrecp2;j2++){
+	    AliITSRecPoint *recp2 = (AliITSRecPoint*)itsRec->At(j2);
+	    recp2->GetGlobalXYZ(gc2);
+	    gc2[0]-=GetNominalPos()[0];
+	    gc2[1]-=GetNominalPos()[1];
+	    Float_t phi2 = TMath::ATan2(gc2[1],gc2[0]);
+	    if(phi2<0)phi2+=TMath::TwoPi();
+
+	    Float_t diff = TMath::Abs(phi2-phi1); 
+	    if(diff>TMath::Pi())diff=TMath::TwoPi()-diff;
+	    if(diff<fDiffPhiMax){
+	      Float_t r1=TMath::Sqrt(gc1[0]*gc1[0]+gc1[1]*gc1[1]);
+	      Float_t zc1=gc1[2];
+	      Float_t erz1=recp1->GetSigmaZ2();
+	      Float_t r2=TMath::Sqrt(gc2[0]*gc2[0]+gc2[1]*gc2[1]);
+	      Float_t zc2=gc2[2];
+	      Float_t erz2=recp2->GetSigmaZ2();
+	      //	Float_t tgth=(zc2[j]-zc1[i])/(r2-r1); // slope (used for multiple scattering)
+	      Float_t zr0=(r2*zc1-r1*zc2)/(r2-r1); //Z @ null radius
+	      Float_t ezr0q=(r2*r2*erz1+r1*r1*erz2)/((r2-r1)*(r2-r1)); //error on Z @ null radius
+	      /*
+	      // Multiple scattering
+	      ezr0q+=r1*r1*(1+tgth*tgth)*theta2L1/2; // multiple scattering in layer 1
+	      ezr0q+=rBP*rBP*(1+tgth*tgth)*theta2BP/2; // multiple scattering in beam pipe
+	      */
+	      if(nopoints<maxdim) new(points[nopoints++])AliITSZPoint(zr0,ezr0q);	      
+	      fZCombc->Fill(zr0);
+	    }
+	  }
+	}
       }
     }
   }
-  delete [] xc1;
-  delete [] yc1;
-  delete [] zc1;
-  delete [] phi1;
-  delete [] xc2;
-  delete [] yc2;
-  delete [] zc2;
-  delete [] phi2;
-  if(fZCombc->GetEntries()==0){
-    Warning("FindVertexForCurrentEvent","Insufficient number of rec. points\n");
+
+  points.Sort();
+
+  Double_t contents = fZCombc->GetEntries()- fZCombc->GetBinContent(0)-fZCombc->GetBinContent(nbincoarse+1);
+  if(contents<1.){
+    //    Warning("FindVertexForCurrentEvent","Insufficient number of rec. points\n");
     ResetHistograms();
-    return fCurrentVertex;
+    fCurrentVertex = new AliESDVertex(startPos,startCov,99999.,-1);
+    points.Clear();
+    return;
   }
-  else {
-    cout<<"Number of entries in hist. "<<fZCombc->GetEntries()<<endl;
+
+  TH1F *hc = fZCombc;
+
+  
+  if(hc->GetBinContent(hc->GetMaximumBin())<3)hc->Rebin(4);
+  Int_t binmin,binmax;
+  Int_t nPeaks=GetPeakRegion(hc,binmin,binmax);   
+  if(nPeaks==2)AliDebug(2,"2 peaks found");
+  Float_t zm =0.;
+  Float_t ezm =0.;
+  Float_t lim1 = hc->GetBinLowEdge(binmin);
+  Float_t lim2 = hc->GetBinLowEdge(binmax)+hc->GetBinWidth(binmax);
+  Float_t widthSR=lim2-lim1;
+
+  if(nPeaks ==1 && (lim2-lim1)<fWindowWidth){
+    Float_t c=(lim1+lim2)/2.;
+    lim1=c-fWindowWidth/2.;
+    lim2=c+fWindowWidth/2.;
   }
-  Int_t bi = fZCombc->GetMaximumBin();
-  Float_t centre = fZCombc->GetBinCenter(bi);
-  Int_t n1 = static_cast<Int_t>((centre-fZCombc->GetBinWidth(bi)-fZCombf->GetBinLowEdge(0))/fZCombf->GetBinWidth(0));
-  Int_t n2 = static_cast<Int_t>((centre+fZCombc->GetBinWidth(bi)-fZCombf->GetBinLowEdge(0))/fZCombf->GetBinWidth(0));
-  Int_t niter = 0;
-  Bool_t goon = kTRUE;
-  Int_t num;
-  while(goon){
-    fZFound = 0.;
-    fZsig = 0.;
-    num=0;
-    for(Int_t n=n1;n<=n2;n++){
-      fZFound+=fZCombf->GetBinCenter(n)*fZCombf->GetBinContent(n);
-      num+=static_cast<Int_t>(fZCombf->GetBinContent(n));
-      fZsig+=fZCombf->GetBinCenter(n)*fZCombf->GetBinCenter(n)*fZCombf->GetBinContent(n);
+  Int_t niter = 0, ncontr=0;
+  do {
+    // symmetrization
+    if(zm  !=0.){
+      Float_t semilarg=TMath::Min((lim2-zm),(zm-lim1));
+      lim1=zm - semilarg;
+      lim2=zm + semilarg;
     }
-    if(num<2){
-      cout<<"ATTENZIONE: num = "<<num<<"; n1= "<<n1<<"; n2 = "<<n2<<endl;
-      fZsig = 0.;
+
+    zm=0.;
+    ezm=0.;
+    ncontr=0;
+    for(Int_t i =0; i<points.GetEntriesFast(); i++){
+      AliITSZPoint* p=(AliITSZPoint*)points.UncheckedAt(i);
+      if(p->GetZ()>lim1 && p->GetZ()<lim2){
+        Float_t deno = p->GetErrZ();
+        zm+=p->GetZ()/deno;
+        ezm+=1./deno;
+        ncontr++;
+      }
     }
-    else {
-      fZsig=TMath::Sqrt(fZsig/(num-1)-fZFound*fZFound/num/(num-1));
-      fZFound/=num;
+    if(ezm>0) {
+      zm/=ezm;
+      ezm=TMath::Sqrt(1./ezm);
     }
-    goon = TMath::Abs(TMath::Abs(fZFound-fZCombf->GetBinCenter(n1))-TMath::Abs(fZFound-fZCombf->GetBinCenter(n2)))>fTolerance;
-    cout<<"Simmetria "<<TMath::Abs(TMath::Abs(fZFound-fZCombf->GetBinCenter(n1))-TMath::Abs(fZFound-fZCombf->GetBinCenter(n2)))<<endl;
-    n1 = static_cast<Int_t>((fZFound-fZCombc->GetBinWidth(bi)-fZCombf->GetBinLowEdge(0))/fZCombf->GetBinWidth(0));
-    n2 = static_cast<Int_t>((fZFound+fZCombc->GetBinWidth(bi)-fZCombf->GetBinLowEdge(0))/fZCombf->GetBinWidth(0));
     niter++;
-    if(niter>=10){
-      goon = kFALSE;
-      Warning("FindVertexForCurrentEvent","The procedure dows not converge\n");
+  } while(niter<10 && TMath::Abs((zm-lim1)-(lim2-zm))>fTolerance);
+  if(nPeaks==2) ezm=widthSR;
+  Double_t position[3]={GetNominalPos()[0],GetNominalPos()[1],zm};
+  Double_t covmatrix[6]={GetNominalCov()[0],0.,GetNominalCov()[2],0.,0.,ezm};
+  fCurrentVertex = new AliESDVertex(position,covmatrix,99999.,ncontr);
+  fCurrentVertex->SetTitle("vertexer: Z");
+  fCurrentVertex->SetDispersion(fDiffPhiMax);
+  fNoVertices=1;
+  points.Clear();
+  if(fSearchForPileup && ncontr>fMinTrackletsForPilup){ 
+    Float_t secPeakPos;
+    Int_t ncontr2=FindSecondPeak(fZCombc,binmin,binmax,secPeakPos);
+    if(ncontr2>=fMinTrackletsForPilup){ 
+      fIsPileup=kTRUE;
+      fNoVertices=2;
+      fZpuv=secPeakPos;
+      fNTrpuv=ncontr2;
+      AliESDVertex secondVert(secPeakPos,0.1,ncontr2);
+      fVertArray = new AliESDVertex[2];
+      fVertArray[0]=(*fCurrentVertex);
+      fVertArray[1]=secondVert;
     }
   }
-  cout<<"Numer of Iterations "<<niter<<endl<<endl;
-  fCurrentVertex = new AliITSVertex(fZFound,fZsig,num);
-  fCurrentVertex->SetTitle("vertexer: B");
+  if(fNoVertices==1){
+    fVertArray = new AliESDVertex[1];
+    fVertArray[0]=(*fCurrentVertex);	  
+  }
+  
   ResetHistograms();
-  return fCurrentVertex;
+  return;
+}
+
+//_____________________________________________________________________
+Int_t AliITSVertexerZ::FindSecondPeak(TH1F* h, Int_t binmin,Int_t binmax, Float_t& secPeakPos){ 
+  // Resets bin contents between binmin and binmax and then search 
+  // for a second peak position 
+  for(Int_t i=binmin-1;i<=binmax+1;i++){
+    h->SetBinContent(i,0.);
+  }
+  Int_t secPeakBin=h->GetMaximumBin();
+  secPeakPos=h->GetBinCenter(secPeakBin);
+  Int_t secPeakCont=(Int_t)h->GetBinContent(secPeakBin);
+  secPeakCont+=(Int_t)h->GetBinContent(secPeakBin-1);
+  secPeakCont+=(Int_t)h->GetBinContent(secPeakBin+1);  
+  secPeakCont+=(Int_t)h->GetBinContent(secPeakBin-2);
+  secPeakCont+=(Int_t)h->GetBinContent(secPeakBin+2);  
+  return secPeakCont;
 }
 
 //_____________________________________________________________________
 void AliITSVertexerZ::ResetHistograms(){
   // delete TH1 data members
   if(fZCombc)delete fZCombc;
-  if(fZCombf)delete fZCombf;
   fZCombc = 0;
-  fZCombf = 0;
-}
-
-//______________________________________________________________________
-void AliITSVertexerZ::FindVertices(){
-  // computes the vertices of the events in the range FirstEvent - LastEvent
-  AliRunLoader *rl = AliRunLoader::GetRunLoader();
-  AliITSLoader* itsLoader =  (AliITSLoader*) rl->GetLoader("ITSLoader");
-  itsLoader->ReloadRecPoints();
-  for(Int_t i=fFirstEvent;i<=fLastEvent;i++){
-    cout<<"Processing event "<<i<<endl;
-    rl->GetEvent(i);
-    FindVertexForCurrentEvent(i);
-    if(fCurrentVertex){
-      WriteCurrentVertex();
-    }
-    else {
-      if(fDebug>0){
-	cout<<"Vertex not found for event "<<i<<endl;
-	cout<<"fZFound = "<<fZFound<<", fZsig= "<<fZsig<<endl;
-      }
-    }
-  }
 }
 
 //________________________________________________________
@@ -322,12 +433,14 @@ void AliITSVertexerZ::PrintStatus() const {
   cout <<fLastL2<<endl;
   cout <<" Max Phi difference: "<<fDiffPhiMax<<endl;
   cout <<"Limits for Z histograms: "<<fLowLim<<"; "<<fHighLim<<endl;
-  cout <<"Bin sizes for coarse and fine z histos "<<fStepCoarse<<"; "<<fStepFine<<endl;
+  cout <<"Bin sizes for coarse z histos "<<fStepCoarse<<endl;
   cout <<" Current Z "<<fZFound<<"; Z sig "<<fZsig<<endl;
-  cout <<" Debug flag: "<<fDebug<<endl;
-  cout <<"First event to be processed "<<fFirstEvent;
-  cout <<"\n Last event to be processed "<<fLastEvent<<endl;
- 
+  if(fZCombc){
+    cout<<"fZCombc exists - entries="<<fZCombc->GetEntries()<<endl;
+  }
+  else{
+    cout<<"fZCombc does not exist\n";
+  }
  
   cout <<"=======================================================\n";
 }