Rivet analyses

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

namespace Rivet {


  /// @brief D*+ polarization
  class CLEO_1991_I314060 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_1991_I314060);


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

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

      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(), "UFS");

      book(_h_ctheta, {0.25, 0.45, 0.55, 0.65, 0.75, 0.85, 1.00});
      for (auto& b : _h_ctheta->bins()) {
        book(b, 2, 1, b.index());
      }

    }

    /// Recursively walk the decay tree to find decay products of @a p
    void findDecayProducts(Particle mother, Particles & d0, Particles & pi,unsigned int & ncount) {
      for (const Particle& p: mother.children()) {
        if(p.abspid()==421) {
          d0.push_back(p);
        }
        else if(p.abspid()==211) {
          pi.push_back(p);
        }
        ncount +=1;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      const double meanBeamMom = ( beams.first.p3().mod() +
                                   beams.second.p3().mod() ) / 2.0;
      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);
      // loop over D*+ mesons
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p: ufs.particles(Cuts::abspid==413)) {
        // calc x+
        double x = (p.momentum().E()+p.momentum().z())/(meanBeamMom + sqrt(sqr(meanBeamMom)+p.mass2()));
        // checck decay products
        Particles d0,pi;
        unsigned int ncount=0;
        findDecayProducts(p,d0, pi,ncount);
        if (ncount!=2 || pi.size()!=1 || d0.size()!=1 ) continue;
        if (pi[0].pid()/p.pid()<0) continue;
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        Vector3 d1 = boost.transform(pi[0].momentum()).p3().unit();
        double ctheta  = d1.dot(p.momentum().p3().unit());
        _h_ctheta->fill(x, ctheta);
      }
    }

    pair<double,pair<double,double> > calcAlpha(const Histo1DPtr& hist) {
      if (hist->numEntries()==0.) return make_pair(0.,make_pair(0.,0.));
      double sum1(0.),sum2(0.),sum3(0.),sum4(0.),sum5(0.);
      for (const auto& bin : hist->bins()) {
        double Oi = bin.sumW();
        if(Oi==0.) continue;
        double a =  1.5*(bin.xMax() - bin.xMin());
        double b = 0.5*(pow(bin.xMax(),3) - pow(bin.xMin(),3));
        double Ei = bin.errW();
        sum1 +=   a*Oi/sqr(Ei);
        sum2 +=   b*Oi/sqr(Ei);
        sum3 += sqr(a)/sqr(Ei);
        sum4 += sqr(b)/sqr(Ei);
        sum5 +=    a*b/sqr(Ei);
      }
      // calculate alpha
      double alpha = (-3*sum1 + 9*sum2 + sum3 - 3*sum5)/(sum1 - 3*sum2 + 3*sum4 - sum5);
      // and error
      double cc = -pow((sum3 + 9*sum4 - 6*sum5),3);
      double bb = -2*sqr(sum3 + 9*sum4 - 6*sum5)*(sum1 - 3*sum2 + 3*sum4 - sum5);
      double aa =  sqr(sum1 - 3*sum2 + 3*sum4 - sum5)*(-sum3 - 9*sum4 + sqr(sum1 - 3*sum2 + 3*sum4 - sum5) + 6*sum5);
      double dis = sqr(bb)-4.*aa*cc;
      if (dis>0.) {
        dis = sqrt(dis);
        return make_pair(alpha,make_pair(0.5*(-bb+dis)/aa,-0.5*(-bb-dis)/aa));
      }
      else {
        return make_pair(alpha,make_pair(0.,0.));
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      //vector<double> x   = {0.35,0.5 ,0.6 ,0.7 ,0.8 ,0.925};
      //vector<double> wid = {0.10,0.05,0.05,0.05,0.05,0.075};
      Estimate1DPtr h_alpha;
      book(h_alpha, 1,1,1);
      Estimate1DPtr h_rho;
      book(h_rho,   1,1,2);
      Estimate1DPtr h_eta;
      book(h_eta,   1,1,3);
      unsigned int ix=0;
      for (auto& b : _h_ctheta->bins()) {
        // normalize
        normalize(b);
        // alpha
        pair<double,pair<double,double> > alpha = calcAlpha(b);
        h_alpha->bin(1+ix).set(alpha.first, alpha.second);
        // rho
        const double rho = (1.+alpha.first)/(3.+alpha.first);
        pair<double,double> rho_error;
        rho_error.first  = 2.*alpha.second.first /sqr(3.+alpha.first);
        rho_error.second = 2.*alpha.second.second/sqr(3.+alpha.first);
        h_rho->bin(1+ix).set(rho, rho_error);
        // eta
        const double eta = alpha.first/(3.+alpha.first);
        pair<double,double> eta_error;
        eta_error.first  = 3.*alpha.second.first /sqr(3.+alpha.first);
        eta_error.second = 3.*alpha.second.second/sqr(3.+alpha.first);
        h_eta->bin(1+ix).set(eta, eta_error);
        ++ix;
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DGroupPtr _h_ctheta;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CLEO_1991_I314060);


}