Rivet analyses

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

namespace Rivet {


  /// @brief B -> K pi pi
  class BABAR_2004_I626730 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2004_I626730);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
      declare(ufs, "UFS");
      DecayedParticles BP(ufs);
      BP.addStable(PID::K0S);
      declare(BP, "BP");
      for (unsigned int ix = 0; ix < 3; ++ix) {
        book(_h_mass2[ix], 2, 1, 1 + ix);
        book(_h_angle[ix], 2, 2, 1 + ix);
        if (ix == 2) continue;
        book(_h_mass[ix], 1, 1, 1 + ix);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{321, 1}, {211, 1}, {-211, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{-321, 1}, {211, 1}, {-211, 1}};
      DecayedParticles BP = apply<DecayedParticles>(event, "BP");
      // loop over particles
      for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
        int sign = BP.decaying()[ix].pid() > 0 ? 1 : -1;
        if ((sign > 0 and BP.modeMatches(ix, 3, mode)) || (sign < 0 and BP.modeMatches(ix, 3, mode))) {
          // boost to B rest frame
          LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
              BP.decaying()[ix].momentum().betaVec());
          // momenta
          FourMomentum pip = boost.transform(BP.decayProducts()[ix].at(211 * sign)[0].momentum());
          FourMomentum pim = boost.transform(BP.decayProducts()[ix].at(-211 * sign)[0].momentum());
          FourMomentum Kp = boost.transform(BP.decayProducts()[ix].at(321 * sign)[0].momentum());
          // mass distributions
          double mKpi = (Kp + pim).mass();
          _h_mass[0]->fill(mKpi);
          double mpipi = (pip + pim).mass();
          _h_mass[1]->fill(mpipi);
          // regions for the helicity analysis
          unsigned int imode = 0;
          if (mKpi > 0.816 && mKpi < 0.976 && mpipi > 1.5)
            imode = 0;
          else if (mpipi > 0.9 && mpipi < 1.1)
            imode = 1;
          else if (mKpi > 0.976 && mKpi < 1.8 && mpipi > 1.5)
            imode = 2;
          else
            continue;
          // pi+pi- resonance
          if (imode == 1) {
            _h_mass2[imode]->fill(mpipi);
            FourMomentum ppipi = pim + pip;
            LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
            double cTheta = boost2.transform(pim).p3().unit().dot(Kp.p3().unit());
            _h_angle[imode]->fill(cTheta);
          }
          // K pi- resonance
          else {
            _h_mass2[imode]->fill(mKpi);
            FourMomentum pKpim = Kp + pim;
            LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pKpim.betaVec());
            double cTheta = boost2.transform(Kp).p3().unit().dot(pip.p3().unit());
            _h_angle[imode]->fill(cTheta);
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 3; ++ix) {
        normalize(_h_mass2[ix], 1., false);
        normalize(_h_angle[ix], 1., false);
        if (ix == 2) continue;
        normalize(_h_mass[ix], 1., false);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mass[2], _h_mass2[3], _h_angle[3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2004_I626730);

}