Rivet analyses

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

namespace Rivet {


  /// @brief D+ -> K- pi+ e+ nu_e
  class BABAR_2010_I879997 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2010_I879997);


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

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

      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid == 411);
      declare(ufs, "UFS");
      DecayedParticles DP(ufs);
      DP.addStable(PID::PI0);
      DP.addStable(PID::K0S);
      DP.addStable(PID::ETA);
      DP.addStable(PID::ETAPRIME);
      declare(DP, "DP");

      // Book histograms
      for (size_t ix = 0; ix < 5; ++ix) {
        book(_h[ix], 1, 1, 1 + ix);
      }
      const vector<double> bins{0., 0.8, 0.9, 1., 1.6};
      for (size_t ix = 0; ix < 4; ++ix) {
        book(_b[ix], bins);
        for (auto& b : _b[ix]->bins()) {
          book(b, 1 + b.index(), 1, 1 + ix);
        }
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{-321, 1}, {211, 1}, {-11, 1}, {12, 1}};
      DecayedParticles DP = apply<DecayedParticles>(event, "DP");
      // loop over particles
      for (unsigned int ix = 0; ix < DP.decaying().size(); ++ix) {
        if (!DP.modeMatches(ix, 4, mode)) continue;
        const Particle& Km = DP.decayProducts()[ix].at(-321)[0];
        const Particle& pip = DP.decayProducts()[ix].at(211)[0];
        const Particle& ep = DP.decayProducts()[ix].at(-11)[0];
        const Particle& nue = DP.decayProducts()[ix].at(12)[0];
        FourMomentum pKstar = Km.momentum() + pip.momentum();
        double mKpi = pKstar.mass();
        _h[4]->fill(mKpi);
        FourMomentum qq = DP.decaying()[ix].momentum() - pKstar;
        double q2 = qq.mass2();
        _h[0]->fill(q2);
        _b[0]->fill(mKpi, q2);
        // boost momenta to DP rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
            DP.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(DP.decaying()[ix].momentum());
        FourMomentum pK = boost.transform(Km.momentum());
        FourMomentum ppi = boost.transform(pip.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();
        double cosK = axisK.dot(pKstar.p3().unit());
        _h[2]->fill(cosK);
        _b[2]->fill(mKpi, cosK);
        LorentzTransform boostW = LorentzTransform::mkFrameTransformFromBeta(qq.betaVec());
        Vector3 axisE = boostW.transform(pe).p3().unit();
        double cosE = axisE.dot(qq.p3().unit());
        _h[3]->fill(cosE);
        _b[3]->fill(mKpi, cosE);
        axisK.setZ(0.);
        axisE.setZ(0.);
        double chi = atan2(axisE.cross(axisK).dot(qq.p3().unit()), axisE.dot(axisK));
        _h[1]->fill(chi);
        _b[1]->fill(mKpi, chi);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h);
      normalize(_b);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[5];
    Histo1DGroupPtr _b[4];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2010_I879997);

}