/data/refman/pasoursint/CMSSW_4_1_8_patch13/src/RecoTauTag/RecoTau/plugins/PFRecoTauDiscriminationByFlightPathSignificance.cc

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#include "RecoTauTag/RecoTau/interface/TauDiscriminationProducerBase.h"
#include "RecoTauTag/TauTagTools/interface/PFTauQualityCutWrapper.h"
#include "FWCore/Utilities/interface/InputTag.h"

/* class PFRecoTauDiscriminationByFlightPathSignificance
 * created : August 30 2010,
 * contributors : Sami Lehti (sami.lehti@cern.ch ; HIP, Helsinki)
 * based on H+ tau ID by Lauri Wendland
 */

#include "TrackingTools/TransientTrack/interface/TransientTrack.h"
#include "TrackingTools/TransientTrack/interface/TransientTrackBuilder.h"
#include "TrackingTools/Records/interface/TransientTrackRecord.h"
#include "RecoVertex/KalmanVertexFit/interface/KalmanVertexFitter.h"
#include "RecoVertex/VertexPrimitives/interface/TransientVertex.h"
#include "RecoBTag/SecondaryVertex/interface/SecondaryVertex.h"

#include "TLorentzVector.h"

using namespace reco;
using namespace std;
using namespace edm;

class PFRecoTauDiscriminationByFlightPathSignificance : public PFTauDiscriminationProducerBase  {
    public:
        explicit PFRecoTauDiscriminationByFlightPathSignificance(const ParameterSet& iConfig):PFTauDiscriminationProducerBase(iConfig),
                                                                               qualityCuts_(iConfig.getParameter<ParameterSet>("qualityCuts")){  // retrieve quality cuts
                flightPathSig           = iConfig.getParameter<double>("flightPathSig");
                withPVError             = iConfig.getParameter<bool>("UsePVerror");

                PVProducer              = iConfig.getParameter<edm::InputTag>("PVProducer");

                booleanOutput           = iConfig.getParameter<bool>("BooleanOutput");
        }

        ~PFRecoTauDiscriminationByFlightPathSignificance(){}

        void beginEvent(const edm::Event&, const edm::EventSetup&);
        double discriminate(const reco::PFTauRef&);

    private:
        double threeProngFlightPathSig(const PFTauRef&);
        double vertexSignificance(reco::Vertex&,reco::Vertex&,GlobalVector&);

        PFTauQualityCutWrapper qualityCuts_;

        double flightPathSig;
        bool withPVError;

        reco::Vertex primaryVertex;
        const TransientTrackBuilder* transientTrackBuilder;
        edm::InputTag PVProducer;

        bool booleanOutput;
};

void PFRecoTauDiscriminationByFlightPathSignificance::beginEvent(const Event& iEvent, const EventSetup& iSetup){

//Primary vertex
        edm::Handle<edm::View<reco::Vertex> > vertexHandle;
        iEvent.getByLabel(PVProducer, vertexHandle);
        const edm::View<reco::Vertex>& vertexCollection(*vertexHandle);

        primaryVertex = *(vertexCollection.begin());

        // Transient Tracks
        edm::ESHandle<TransientTrackBuilder> builder;
        iSetup.get<TransientTrackRecord>().get("TransientTrackBuilder",builder);
        transientTrackBuilder = builder.product();

}

double PFRecoTauDiscriminationByFlightPathSignificance::discriminate(const PFTauRef& tau){

        if(booleanOutput) return ( threeProngFlightPathSig(tau) > flightPathSig ? 1. : 0. );
        return threeProngFlightPathSig(tau);
}

double PFRecoTauDiscriminationByFlightPathSignificance::threeProngFlightPathSig(const PFTauRef& tau){
        double flightPathSignificance = 0;

//Secondary vertex
        const PFCandidateRefVector pfSignalCandidates = tau->signalPFChargedHadrCands();
        vector<TransientTrack> transientTracks;
        RefVector<PFCandidateCollection>::const_iterator iTrack;
        for(iTrack = pfSignalCandidates.begin(); iTrack!= pfSignalCandidates.end(); iTrack++){
                const PFCandidate& pfCand = *(iTrack->get());
                if(pfCand.trackRef().isNonnull()){
                  const TransientTrack transientTrack = transientTrackBuilder->build(pfCand.trackRef());
                  transientTracks.push_back(transientTrack);
                }
        }
        if(transientTracks.size() > 1){
                KalmanVertexFitter kvf(true);
                TransientVertex tv = kvf.vertex(transientTracks);

                if(tv.isValid()){
                        GlobalVector tauDir(tau->px(),
                                            tau->py(),
                                            tau->pz());
                        Vertex secVer = tv;
                        flightPathSignificance = vertexSignificance(primaryVertex,secVer,tauDir);
                }
        }
        return flightPathSignificance;
}

double PFRecoTauDiscriminationByFlightPathSignificance::vertexSignificance(reco::Vertex& pv, Vertex& sv,GlobalVector& direction){
        return SecondaryVertex::computeDist3d(pv,sv,direction,withPVError).significance();
}

DEFINE_FWK_MODULE(PFRecoTauDiscriminationByFlightPathSignificance);