Rivet analyses

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

namespace Rivet {


  /// @brief q^2 in D_s+ -> K0 e+ nu_e and ->K*0 e+ nu_e distributions
  class BESIII_2019_I1702549 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1702549);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 431);
      declare(ufs, "UFS");
      DecayedParticles DS(ufs);
      DS.addStable(PID::PI0);
      DS.addStable(PID::K0S);
      DS.addStable(PID::ETA);
      DS.addStable(PID::ETAPRIME);
      declare(DS, "DS");

      // Book histograms
      book(_h_q2, 1, 1, 1);
      book(_nD, "/TMP/nD");
      for (unsigned int ix = 0; ix < 5; ++ix) book(_h_Kstar[ix], 1, 1, 3 + ix);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode1 = {{310, 1}, {-11, 1}, {12, 1}};
      static const map<PdgId, unsigned int>& mode2 = {{130, 1}, {-11, 1}, {12, 1}};
      static const map<PdgId, unsigned int>& mode3 = {{311, 1}, {-11, 1}, {12, 1}};
      static const map<PdgId, unsigned int>& mode4 = {{321, 1}, {-211, 1}, {-11, 1}, {12, 1}};
      DecayedParticles DS = apply<DecayedParticles>(event, "DS");
      // loop over particles
      for (unsigned int ix = 0; ix < DS.decaying().size(); ++ix) {
        _nD->fill();
        if (DS.modeMatches(ix, 3, mode1)) {
          _h_q2->fill((DS.decaying()[ix].momentum() - DS.decayProducts()[ix].at(310)[0].momentum()).mass2());
        }
        else if (DS.modeMatches(ix, 3, mode2)) {
          _h_q2->fill((DS.decaying()[ix].momentum() - DS.decayProducts()[ix].at(130)[0].momentum()).mass2());
        }
        else if (DS.modeMatches(ix, 3, mode3)) {
          _h_q2->fill((DS.decaying()[ix].momentum() - DS.decayProducts()[ix].at(311)[0].momentum()).mass2());
        }
        else if (DS.modeMatches(ix, 4, mode4)) {
          const Particle& Kp = DS.decayProducts()[ix].at(321)[0];
          const Particle& pim = DS.decayProducts()[ix].at(-211)[0];
          const Particle& ep = DS.decayProducts()[ix].at(-11)[0];
          const Particle& nue = DS.decayProducts()[ix].at(12)[0];
          FourMomentum pKstar = Kp.momentum() + pim.momentum();
          _h_Kstar[0]->fill(pKstar.mass());
          FourMomentum qq = DS.decaying()[ix].momentum() - pKstar;
          _h_Kstar[1]->fill(qq.mass2());
          // boost momenta to Ds rest frame
          LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
              DS.decaying()[ix].momentum().betaVec());
          FourMomentum pKS = boost.transform(pKstar);
          Matrix3 ptoz(-pKS.p3().unit(), Vector3(0, 0, 1));
          boost.preMult(ptoz);
          // the momenta in frane to W along z
          FourMomentum pD = boost.transform(DS.decaying()[ix].momentum());
          FourMomentum pK = boost.transform(Kp.momentum());
          FourMomentum ppi = boost.transform(pim.momentum());
          FourMomentum pe = boost.transform(ep.momentum());
          FourMomentum pnu = boost.transform(nue.momentum());
          pKstar = pK + ppi;
          qq = pD - pKstar;
          LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
          Vector3 axisK = boostK.transform(pK).p3().unit();
          _h_Kstar[3]->fill(axisK.dot(pKstar.p3().unit()));
          LorentzTransform boostW = LorentzTransform::mkFrameTransformFromBeta(qq.betaVec());
          Vector3 axisE = boostW.transform(pe).p3().unit();
          _h_Kstar[2]->fill(axisE.dot(qq.p3().unit()));
          axisK.setZ(0.);
          axisE.setZ(0.);
          double chi = atan2(axisE.cross(axisK).dot(qq.p3().unit()), axisE.dot(axisK));
          _h_Kstar[4]->fill(chi);
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // normalise to width in inverse ns
      scale(_h_q2, 1. / 0.504e-3 / *_nD);
      for (unsigned int ix = 0; ix < 5; ++ix) {
        normalize(_h_Kstar[ix]);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_q2;
    Histo1DPtr _h_Kstar[5];
    CounterPtr _nD;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2019_I1702549);

}