/data/refman/pasoursint/CMSSW_4_1_8_patch9/src/RecoBTag/SecondaryVertex/interface/SimpleSecondaryVertexComputer.h

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#ifndef RecoBTag_SecondaryVertex_SimpleSecondaryVertexComputer_h
#define RecoBTag_SecondaryVertex_SimpleSecondaryVertexComputer_h

#include <cmath>

#include "Math/GenVector/VectorUtil.h"

#include "DataFormats/TrackReco/interface/Track.h"
#include "DataFormats/VertexReco/interface/Vertex.h"
#include "DataFormats/BTauReco/interface/SecondaryVertexTagInfo.h"

#include "RecoBTau/JetTagComputer/interface/JetTagComputer.h"

#include "RecoBTag/SecondaryVertex/interface/TrackKinematics.h"

class SimpleSecondaryVertexComputer : public JetTagComputer {
    public:
        SimpleSecondaryVertexComputer(const edm::ParameterSet &parameters) :
                use2d(!parameters.getParameter<bool>("use3d")),
                useSig(parameters.getParameter<bool>("useSignificance")),
                unBoost(parameters.getParameter<bool>("unBoost")),
                minTracks(parameters.getParameter<unsigned int>("minTracks"))
        { uses("svTagInfos"); }

        float discriminator(const TagInfoHelper &tagInfos) const
        {
                const reco::SecondaryVertexTagInfo &info =
                                tagInfos.get<reco::SecondaryVertexTagInfo>();
                unsigned int idx = 0;
                while(idx < info.nVertices()) {
                        if (info.nVertexTracks(idx) >= minTracks)
                                break;
                        idx++;
                }
                if (idx >= info.nVertices())
                        return -1.0;

                double gamma;
                if (unBoost) {
                        reco::TrackKinematics kinematics(
                                                info.secondaryVertex(idx));
                        gamma = kinematics.vectorSum().Gamma();
                } else
                        gamma = 1.0;

                double value;
                if (useSig)
                        value = info.flightDistance(idx, use2d).significance();
                else
                        value = info.flightDistance(idx, use2d).value();

                value /= gamma;

                if (useSig)
                        value = (value > 0) ? +std::log(1 + value)
                                            : -std::log(1 - value);

                return value;
        }

    private:
        bool            use2d;
        bool            useSig;
        bool            unBoost;
        unsigned int    minTracks;
};

#endif // RecoBTag_SecondaryVertex_SimpleSecondaryVertexComputer_h