Rivet analyses

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

namespace Rivet {


  /// @brief B* production at LEP1
  class OPAL_1996_I428493 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_1996_I428493);


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

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

      // // Initialise and register projections
      declare(ChargedFinalState(), "FS");
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_ctheta1, 3, 1, 1);
      book(_h_ctheta2, "/TMP/ctheta", 20, -1., 1.);
      book(_c_hadron, "/TMP/chadron");
      book(_c_bStar, "/TMP/cbStar ", refData<YODA::BinnedEstimate<string>>(1, 1, 1));
      book(_c_B, "/TMP/cB     ", refData<YODA::BinnedEstimate<string>>(1, 1, 1));
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // First, veto on leptonic events by requiring at least 4 charged FS particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      const size_t numParticles = fs.particles().size();

      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
      if (numParticles < 2) {
        MSG_DEBUG("Failed leptonic event cut");
        vetoEvent;
      }
      MSG_DEBUG("Passed leptonic event cut");

      _c_hadron->fill();
      // loop over the particles
      for (const Particle& p : apply<UnstableParticles>(event, "UFS")
                                   .particles(Cuts::abspid == 513 or Cuts::abspid == 523
                                              or Cuts::abspid == 511 or Cuts::abspid == 521)) {
        int sign = p.pid() / p.abspid();
        // count number of Bs not from mixing or B*
        if (p.abspid() == 511 || p.abspid() == 521) {
          if (p.parents()[0].abspid() == p.abspid()) continue;
          if (p.parents()[0].abspid() == 513 || p.parents()[0].abspid() == 523) continue;
          _c_B->fill("91.2"s);
        }
        // B*
        else {
          _c_bStar->fill("91.2"s);
          Particle decay;
          if (p.children().size() != 2) continue;
          int mid = p.abspid() - 2;
          if (p.children()[0].pid() == sign * mid && p.children()[1].pid() == 22) {
            decay = p.children()[1];
          }
          else if (p.children()[1].pid() == sign * mid && p.children()[0].pid() == 22) {
            decay = p.children()[0];
          }
          else
            continue;
          LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
          Vector3 e1z = p.p3().unit();
          FourMomentum pp = boost.transform(decay.momentum());
          Vector3 axis1 = boost.transform(decay.momentum()).p3().unit();
          double ctheta = e1z.dot(axis1);
          _h_ctheta1->fill(ctheta);
          _h_ctheta2->fill(ctheta);
        }
      }
    }

    pair<double, double> calcRho(Histo1DPtr hist) {
      if (hist->numEntries() == 0.) return make_pair(0., 0.);
      double sum1(0.), sum2(0.);
      for (const auto& bin : hist->bins()) {
        double Oi = bin.sumW();
        if (Oi == 0.) continue;
        double ai = 0.125 * (-bin.xMin() * (3. + sqr(bin.xMin())) + bin.xMax() * (3. + sqr(bin.xMax())));
        double bi = 0.375 * (-bin.xMin() * (1. - sqr(bin.xMin())) + bin.xMax() * (1. - sqr(bin.xMax())));
        double Ei = bin.errW();
        sum1 += sqr(bi / Ei);
        sum2 += bi / sqr(Ei) * (Oi - ai);
      }
      return make_pair(sum2 / sum1, sqrt(1. / sum1));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // polarization
      scale(_h_ctheta1, 1. / _c_hadron->val());
      normalize(_h_ctheta2);
      pair<double, double> rho = calcRho(_h_ctheta2);
      BinnedEstimatePtr<string> h_rho;
      book(h_rho, 2, 1, 1);
      h_rho->bin(1).set(rho.first, rho.second);
      BinnedEstimatePtr<string> h1;
      book(h1, 1, 1, 1);
      // no of B*/B+B*
      divide(*_c_bStar, *_c_bStar + *_c_B, h1);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_ctheta1, _h_ctheta2;
    CounterPtr _c_hadron;
    BinnedHistoPtr<string> _c_bStar, _c_B;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(OPAL_1996_I428493);


}