Rivet analyses

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

namespace Rivet {


  /// @brief Spectrum for D_s1
  class CLEOII_1993_I352823 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_1993_I352823);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(), "UFS");
      // book histos
      book(_h_x, 3, 1, 1);
      book(_h_cTheta, 4, 1, 1);
      book(_r[0], 2, 1, 1);
      book(_r[1], 2, 1, 2);
    }

    bool isK0(int id) {
      return id == 310 || id == 130 || abs(id) == 311;
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const int DsID = 10433;
      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      const double Emax = (beams.first.p3().mod() + beams.second.p3().mod()) / 2.0;
      const double Pmax = sqrt(sqr(Emax) - sqr(2.535));
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::abspid == DsID)) {
        // spectrum
        double xp = p.momentum().p3().mod() / Pmax;
        _h_x->fill(xp);
        // decay angle
        int sign = p.pid() / DsID;
        Particle Dstar;
        if (p.children().size() != 2) continue;
        if (p.children()[0].pid() == sign * 423 && p.children()[1].pid() == sign * 321) {
          Dstar = p.children()[0];
        }
        else if (p.children()[1].pid() == sign * 423 && p.children()[0].pid() == sign * 321) {
          Dstar = p.children()[1];
        }
        else if (p.children()[0].pid() == sign * 413 && isK0(p.children()[1].pid())) {
          _r[1]->fill(">= 0.0"s);
          continue;
        }
        else if (p.children()[1].pid() == sign * 413 && isK0(p.children()[0].pid())) {
          _r[1]->fill(">= 0.0"s);
          continue;
        }
        else {
          continue;
        }
        _r[0]->fill(">= 0.0"s);
        if (Dstar.children().size() != 2) continue;
        Particle pion;
        if (Dstar.children()[0].pid() == 111 && Dstar.children()[1].pid() == sign * 421) {
          pion = Dstar.children()[0];
        }
        else if (Dstar.children()[1].pid() == 111 && Dstar.children()[0].pid() == sign * 421) {
          pion = Dstar.children()[1];
        }
        else
          continue;
        // first boost to the D_s1 rest frame
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        FourMomentum pDstar = boost1.transform(Dstar.momentum());
        FourMomentum pPion = boost1.transform(pion.momentum());
        // to D* rest frame
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
        Vector3 axis = pDstar.p3().unit();
        FourMomentum pp = boost2.transform(pPion);
        // calculate angle
        double cTheta = pp.p3().unit().dot(axis);
        _h_cTheta->fill(cTheta);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_x);
      normalize(_h_cTheta);
      scale(_r[0], crossSection() / sumOfWeights() / picobarn);
      scale(_r[1], crossSection() / sumOfWeights() / picobarn);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_x, _h_cTheta;
    BinnedHistoPtr<string> _r[2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CLEOII_1993_I352823);

}