Rivet analyses

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

namespace Rivet {


  /// @brief B -> Xs l+l-
  class BELLE_2016_I1283183 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2016_I1283183);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::abspid == 521 || Cuts::abspid == 511), "UFS");
      // book the profile hist
      for (unsigned int ix = 0; ix < 4; ++ix) book(_p[ix], 1, 1, ix + 1);
    }

    void findDecayProducts(bool& charm,
                           const Particle& mother,
                           unsigned int& nK0,
                           unsigned int& nKp,
                           unsigned int& nKm,
                           Particles& lp,
                           Particles& lm) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (PID::isCharmHadron(p.pid()))
          charm = true;
        else if (id == PID::POSITRON || id == PID::ANTIMUON)
          lp.push_back(p);
        else if (id == PID::ELECTRON || id == PID::MUON)
          lm.push_back(p);
        else if (id == PID::KPLUS)
          ++nKp;
        else if (id == PID::KMINUS)
          ++nKm;
        else if (id == PID::K0S)
          ++nK0;
        else if (id == PID::PI0 || id == PID::PIPLUS || id == PID::PIMINUS) {
          continue;
        }
        else if (!p.children().empty()) {
          findDecayProducts(charm, p, nK0, nKp, nKm, lp, lm);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      if (_edges.empty()) {
        for (unsigned int ix = 0; ix < 4; ++ix) _edges.push_back(_p[ix]->xEdges()[0]);
      }
      // Loop over bottoms
      for (const Particle& bottom : apply<UnstableParticles>(event, "UFS").particles()) {
        // remove mixing entries etc
        if (bottom.children()[0].abspid() == bottom.abspid()) continue;
        bool charm = false;
        Particles lp, lm;
        unsigned int nK0(0), nKp(0), nKm(0);
        findDecayProducts(charm, bottom, nK0, nKp, nKm, lp, lm);
        if (charm) continue;
        unsigned int nk = nKp - nKm + nK0;
        if (nk % 2 == 0) continue;
        if (lp.size() != 1 || lm.size() != 1 || lp[0].pid() != -lm[0].pid()) continue;
        if (bottom.pid() > 0) swap(lp, lm);
        double q2 = (lp[0].momentum() + lm[0].momentum()).mass2();
        // veto region valid for muons but not electrons
        if (lm[0].pid() == PID::ELECTRON && ((q2 > 7.3 && q2 < 10.5) || (q2 > 11.8 && q2 < 12.5))) continue;
        // first boost to bottom frame
        const LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
            bottom.momentum().betaVec());
        FourMomentum plp = boost.transform(lp[0].momentum());
        FourMomentum plm = boost.transform(lm[0].momentum());
        FourMomentum pB = boost.transform(bottom.momentum());
        const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta((plp + plm).betaVec());
        plp = boost2.transform(plp);
        pB = boost.transform(pB);
        double cTheta = plp.p3().unit().dot(pB.p3().unit());
        if (q2 > 0.2 && q2 < 4.3)
          _p[0]->fill(_edges[0], cTheta > 0 ? 1 : -1);
        else if (q2 > 4.3 && q2 < 8.1)
          _p[1]->fill(_edges[1], cTheta > 0 ? 1 : -1);
        else if (q2 > 10.2 && q2 < 12.5)
          _p[2]->fill(_edges[2], cTheta > 0 ? 1 : -1);
        else if (q2 > 14.3 && q2 < 25.0)
          _p[3]->fill(_edges[3], cTheta > 0 ? 1 : -1);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() { }

    /// @}


    /// @name Histograms
    /// @{
    BinnedProfilePtr<string> _p[4];
    vector<string> _edges;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2016_I1283183);

}