PixelVertexProducerMedian.cc

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#include "PixelVertexProducerMedian.h"

#include "FWCore/Framework/interface/MakerMacros.h"
#include "FWCore/Framework/interface/ESHandle.h"
#include "FWCore/Framework/interface/Frameworkfwd.h"
#include "FWCore/Framework/interface/Event.h"

#include "DataFormats/TrackReco/interface/Track.h"
#include "DataFormats/TrackReco/interface/TrackFwd.h"

#include "DataFormats/VertexReco/interface/Vertex.h"
#include "DataFormats/VertexReco/interface/VertexFwd.h"

#include <fstream>
#include <iostream>
#include <vector>
#include <algorithm>

#include "TROOT.h"
#include "TH1F.h"
#include "TF1.h"

/*****************************************************************************/
struct ComparePairs
{
  bool operator() (const reco::Track * t1,
                   const reco::Track * t2)
  {
    return (t1->vz() < t2->vz());
  };
};

/*****************************************************************************/
PixelVertexProducerMedian::PixelVertexProducerMedian
  (const edm::ParameterSet& ps) : theConfig(ps)
{
  produces<reco::VertexCollection>();
}


/*****************************************************************************/
PixelVertexProducerMedian::~PixelVertexProducerMedian()
{ 
}

/*****************************************************************************/
void PixelVertexProducerMedian::produce
  (edm::Event& ev, const edm::EventSetup& es)
{
  // Get pixel tracks
  edm::Handle<reco::TrackCollection> trackCollection;
  std::string trackCollectionName =
    theConfig.getParameter<std::string>("TrackCollection");
  ev.getByLabel(trackCollectionName, trackCollection);
  const reco::TrackCollection tracks_ = *(trackCollection.product());

  thePtMin = theConfig.getParameter<double>("PtMin");

  // Select tracks 
  std::vector<const reco::Track *> tracks;
  for (unsigned int i=0; i<tracks_.size(); i++)
  {
    if (tracks_[i].pt() > thePtMin)
    {
      reco::TrackRef recTrack(trackCollection, i);
      tracks.push_back( &(*recTrack));
    }
  }

  LogTrace("MinBiasTracking")
            << " [VertexProducer] selected tracks: "
            << tracks.size() << " (out of " << tracks_.size()
            << ")"; 

  auto vertices = std::make_unique<reco::VertexCollection>();

  if(!tracks.empty())
  {
  // Sort along vertex z position
  std::sort(tracks.begin(), tracks.end(), ComparePairs());
  
  // Median
  float med;
  if(tracks.size() % 2 == 0)
    med = (tracks[tracks.size()/2-1]->vz() + tracks[tracks.size()/2]->vz())/2;
  else
    med =  tracks[tracks.size()/2  ]->vz();

  LogTrace("MinBiasTracking")
   << "  [vertex position] median    = " << med << " cm";

  if(tracks.size() > 10)
  {
    // Binning around med, halfWidth
    int nBin = 100;
    float halfWidth = 0.1; // cm
  
    // Most probable
    TH1F histo("histo","histo", nBin, -halfWidth,halfWidth);
  
    for(std::vector<const reco::Track *>::const_iterator
        track = tracks.begin(); track!= tracks.end(); track++)
      if(fabs((*track)->vz() - med) < halfWidth)
        histo.Fill((*track)->vz() - med);
  
    LogTrace("MinBiasTracking")
              << "  [vertex position] most prob = "
              << med + histo.GetBinCenter(histo.GetMaximumBin())
              << " cm";
  
    // Fit above max/2
    histo.Sumw2();
  
    TF1 f1("f1","[0]*exp(-0.5 * ((x-[1])/[2])^2) + [3]");
    f1.SetParameters(10.,0.,0.01, 1.);
  
    histo.Fit(&f1,"QN");
  
    LogTrace("MinBiasTracking")
              << "  [vertex position] fitted    = "
              << med + f1.GetParameter(1) << " +- " << f1.GetParError(1)
              << " cm";
    
    // Store
    reco::Vertex::Error err;
    err(2,2) = f1.GetParError(1) * f1.GetParError(1); 
    reco::Vertex ver(reco::Vertex::Point(0,0,med + f1.GetParameter(1)),
                                         err, 0, 1, 1);
    vertices->push_back(ver);
  }
  else
  {
    // Store
    reco::Vertex::Error err;
    err(2,2) = 0.1 * 0.1;
    reco::Vertex ver(reco::Vertex::Point(0,0,med),
                                         err, 0, 1, 1);
    vertices->push_back(ver);
  }
  }
  ev.put(std::move(vertices));
}