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