Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Bbar0 -> J/[psi K- pi+
  class BELLE_2014_I1312626 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2014_I1312626);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
      declare(ufs, "UFS");
      DecayedParticles B0(ufs);
      B0.addStable(443);
      declare(B0, "B0");
      // histograms
      for (unsigned int ix = 0; ix < 7; ++ix) book(_h_mass[ix], 1, 1, 1 + ix);
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h_angle[ix], 2, 1, 1 + ix);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{211, 1}, {-321, 1}, {443, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{-211, 1}, {321, 1}, {443, 1}};
      DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
      for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
        int sign = 1;
        if (B0.decaying()[ix].pid() < 0 && B0.modeMatches(ix, 3, mode)) sign = 1;
        if (B0.decaying()[ix].pid() > 0 && B0.modeMatches(ix, 3, modeCC))
          sign = -1;
        else
          continue;
        const Particle& pip = B0.decayProducts()[ix].at(sign * 211)[0];
        const Particle& Km = B0.decayProducts()[ix].at(-sign * 321)[0];
        const Particle& JPsi = B0.decayProducts()[ix].at(443)[0];
        double mpiJ2 = (pip.momentum() + JPsi.momentum()).mass2();
        double mKpi2 = (pip.momentum() + Km.momentum()).mass2();
        if (mpiJ2 < 16.)
          _h_mass[0]->fill(mKpi2);
        else if (mpiJ2 < 19.)
          _h_mass[1]->fill(mKpi2);
        else
          _h_mass[2]->fill(mKpi2);
        if (mKpi2 < 1.2)
          _h_mass[3]->fill(mpiJ2);
        else if (mKpi2 < 2.05)
          _h_mass[4]->fill(mpiJ2);
        else if (mKpi2 < 3.2)
          _h_mass[5]->fill(mpiJ2);
        else
          _h_mass[6]->fill(mpiJ2);
        // mass cuts for angular variables
        if (mKpi2 < 1.2 || mpiJ2 < 16. || mpiJ2 > 19.) continue;
        // helicity angle find J.psi leptonic children
        if (JPsi.children().size() != 2) continue;
        if (JPsi.children()[0].pid() != -JPsi.children()[1].pid()) continue;
        if (JPsi.children()[0].abspid() != PID::EMINUS && JPsi.children()[0].abspid() != PID::MUON) continue;
        Particle lm = JPsi.children()[0];
        Particle lp = JPsi.children()[1];
        if (lm.pid() < 0) swap(lm, lp);
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
            B0.decaying()[ix].momentum().betaVec());
        FourMomentum ppsi = boost1.transform(JPsi.momentum());
        Vector3 axis1 = -ppsi.p3().unit();
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppsi.betaVec());
        FourMomentum plp = boost2.transform(boost1.transform(lp.momentum()));
        double cL = plp.p3().unit().dot(axis1);
        _h_angle[0]->fill(cL);
        Vector3 LTrans = plp.p3() - cL * plp.p3().mod() * axis1;
        FourMomentum pKpi = boost1.transform(pip.momentum() + Km.momentum());
        LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pKpi.betaVec());
        FourMomentum ppi = boost3.transform(boost1.transform(pip.momentum()));
        double cPi = ppi.p3().unit().dot(axis1);
        Vector3 PTrans = ppi.p3() - cPi * ppi.p3().mod() * axis1;
        double phi = atan2(LTrans.cross(PTrans).dot(axis1), LTrans.dot(PTrans));
        _h_angle[1]->fill(phi);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 7; ++ix) normalize(_h_mass[ix], 1., false);
      for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h_angle[ix], 1., false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mass[7], _h_angle[2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2014_I1312626);

}