Rivet analyses

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

namespace Rivet {


  /// @brief  e+e- > tau+ tau-
  class OPAL_2001_I554583 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_2001_I554583);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(ChargedFinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      // book histos
      const vector<double> edges{-0.9, -0.72, -0.54, -0.36, -0.18, 0., 0.18, 0.36, 0.54, 0.72, 0.9};
      book(_h_e, edges);
      book(_h_mu, edges);
      book(_h_pi, edges);
      book(_h_rho, edges);
      for (size_t ix=0; ix<_h_e->numBins(); ++ix) {
        const string suff = std::to_string(ix);
        book(_h_e->bin(ix+1), "_h_e_"+suff, 20, -1.0, 1.0);
        book(_h_mu->bin(ix+1), "_h_mu_"+suff, 20, -1.0, 1.0);
        book(_h_pi->bin(ix+1), "_h_pi_"+suff, 20, -1.0, 1.0);
        book(_h_rho->bin(ix+1), "_h_rho_"+suff, 20, -1.0, 1.0);
      }
      book(_t_e  ,"_t_e " , 20,-1,1);
      book(_t_mu ,"_t_mu" , 20,-1,1);
      book(_t_pi ,"_t_pi" , 20,-1,1);
      book(_t_rho,"_t_rho", 20,-1,1);
    }

    void findTau(const Particle & p, unsigned int & nprod, Particles& piP,
                     Particles& pi0, Particles& ell, Particles& nu_ell, Particles& nu_tau) {
      for (const Particle & child : p.children()) {
        if(child.pid()==PID::ELECTRON || child.pid()==PID::MUON) {
          ++nprod;
          ell.push_back(child);
        }
        else if(child.pid()==PID::NU_EBAR || child.pid()==PID::NU_MUBAR) {
          ++nprod;
          nu_ell.push_back(child);
        }
        else if(child.pid()==PID::PIMINUS) {
          ++nprod;
          piP.push_back(child);
        }
        else if(child.pid()==PID::PI0) {
          ++nprod;
          pi0.push_back(child);
        }
        else if(child.pid()==PID::NU_TAU) {
          ++nprod;
          nu_tau.push_back(child);
        }
        else if(child.pid()==PID::GAMMA) {
          continue;
        }
        else if(child.children().empty() || child.pid()==221 || child.pid()==331) {
          ++nprod;
        }
        else {
          findTau(child,nprod,piP,pi0,ell,nu_ell,nu_tau);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // require 2 chanrged particles to veto hadronic events
      if(apply<ChargedFinalState>(event, "FS").particles().size()!=2) vetoEvent;
      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      if (beams.first.pid()>0) {
        axis = beams.first .momentum().p3().unit();
      }
      else {
        axis = beams.second.momentum().p3().unit();
      }
      // loop over tau leptons
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==15)) {
        unsigned int nprod(0);
        Particles piP, pi0, ell, nu_ell, nu_tau;
        findTau(p,nprod,piP, pi0, ell, nu_ell, nu_tau);
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        double cBeam = axis.dot(p.momentum().p3().unit());
        if (nprod==2 && nu_tau.size()==1 && piP.size()==1) {
          FourMomentum pPi = boost1.transform(piP[0].momentum());
          double cTheta = pPi.p3().unit().dot(p.momentum().p3().unit());
          _h_pi->fill(cBeam, cTheta);
          _t_pi->fill(cTheta);
        }
        else if (nprod==3 && nu_tau.size()==1 && ell.size()==1 && nu_ell.size()==1) {
          if (ell[0].pid()==PID::ELECTRON) {
            _h_e->fill(cBeam,2.*ell[0].momentum().t()/sqrtS());
            _t_e ->fill(2.*ell[0].momentum().t()/sqrtS());
          }
          else {
            _h_mu->fill(cBeam,2.*ell[0].momentum().t()/sqrtS());
            _t_mu->fill(2.*ell[0].momentum().t()/sqrtS());
          }
        }
        else if(nprod==3 && nu_tau.size()==1 && piP.size()==1&& pi0.size()==1) {
          FourMomentum pRho = boost1.transform(piP[0].momentum()+pi0[0].momentum());
          double cTheta = pRho.p3().unit().dot(p.momentum().p3().unit());
          _h_rho->fill(cBeam, cTheta);
          _t_rho->fill(cTheta);
        }
      }
    }

    pair<double,double> calcP(Histo1DPtr hist,unsigned int imode) {
      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.),bi(0.);
        // tau -> pi/rho nu
        if(imode==0) {
          ai = 0.5*(bin.xMax()-bin.xMin());
          bi = 0.5*ai*(bin.xMax()+bin.xMin());
        }
        // lepton mode
        else {
          ai = (-5*bin.xMin() + 3*pow(bin.xMin(),3) -   pow(bin.xMin(),4) + 5*bin.xMax() - 3*pow(bin.xMax(),3) +   pow(bin.xMax(),4))/3.;
          bi = (  -bin.xMin() + 3*pow(bin.xMin(),3) - 2*pow(bin.xMin(),4) +   bin.xMax() - 3*pow(bin.xMax(),3) + 2*pow(bin.xMax(),4))/3.;
        }
        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() {
      Estimate1DPtr _h_P;
      book(_h_P,2,1,1);
      BinnedEstimatePtr<string> _t_P;
      book(_t_P,1,1,5);
      for (size_t ix=0; ix < _h_e->numBins()+1; ++ix) {
        Histo1DPtr& he = ix<10 ? _h_e->bin(ix+1) : _t_e;
        normalize(he);
        pair<double,double> P_e  = calcP(he, 1);
        double s1 = P_e.first/sqr(P_e.second);
        double s2 = 1./sqr(P_e.second);
        Histo1DPtr& hmu = ix<10 ? _h_mu->bin(ix+1) : _t_mu;
        normalize(hmu);
        pair<double,double> P_mu = calcP(hmu,1);
        s1 += P_mu.first/sqr(P_mu.second);
        s2 += 1./sqr(P_mu.second);
        Histo1DPtr& hpi = ix<10 ? _h_pi->bin(ix+1) : _t_pi;
        normalize(hpi);
        pair<double,double> P_pi = calcP(hpi,0);
        s1 += P_pi.first/sqr(P_pi.second);
        s2 += 1./sqr(P_pi.second);
        Histo1DPtr& hrho = ix<10 ? _h_rho->bin(ix+1) : _t_rho;
        normalize(hrho);
        pair<double,double> P_rho = calcP(hrho,0);
    P_rho.first  /=0.46;
    P_rho.second /=0.46;
        s1 += P_rho.first/sqr(P_rho.second);
        s2 += 1./sqr(P_rho.second);
        // average
        if(ix<10)
          _h_P->bin(ix+1).set(s1/s2, sqrt(1./s2));
        else
      _t_P->bin(1).set(s1/s2,sqrt(1./s2));
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DGroupPtr _h_e,_h_mu,_h_pi,_h_rho;
    Histo1DPtr      _t_e,_t_mu,_t_pi,_t_rho;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(OPAL_2001_I554583);

}