Rivet analyses

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

namespace Rivet {


  /// @brief J/psi and psi(2s) -> Xi* and Sigma*
  class BESIII_2017_I1506414 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1506414);


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

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

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

      // Book histograms
      size_t ih = 0;
      for (double eVal : allowedEnergies()) {

        const string en = toString(round(eVal/MeV));
        if (isCompatibleWithSqrtS(eVal, 1e-1))  _sqs = en;

        book(_h[en+"sig"], 1, 1, 1+ih);
        book(_h[en+"xi"],  1, 1, 2+ih);
        ih += 2;
      }
      raiseBeamErrorIf(_sqs.empty());
    }

    void findChildren(const Particle& p,map<long,int>& nRes, int &ncount) const {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          nRes[child.pid()]-=1;
          --ncount;
        }
        else {
          findChildren(child,nRes,ncount);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // get the axis, direction of incoming electron
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      if (beams.first.pid()>0) axis = beams.first .mom().p3().unit();
      else                     axis = beams.second.mom().p3().unit();
      // types of final state particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }


      const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p :  ufs.particles(Cuts::abspid==3322 or Cuts::abspid==3214)) {
        if (p.children().empty()) continue;
        map<long,int> nRes=nCount;
        int ncount = ntotal;
        findChildren(p,nRes,ncount);
        bool matched=false;
        // check for antiparticle
        for (const Particle& p2 :  ufs.particles(Cuts::pid==-p.pid())) {
          if (p2.children().empty()) continue;
          map<long,int> nRes2=nRes;
          int ncount2 = ncount;
          findChildren(p2,nRes2,ncount2);
          if (ncount2==0) {
            matched = true;
            for (const auto& val : nRes2) {
              if (val.second!=0) {
                matched = false;
                break;
              }
            }
            // found baryon and antibaryon
            if (matched) {
              // calc cosine
              double ctheta;
              if (p.pid()>0)  ctheta = p .mom().p3().unit().dot(axis);
              else            ctheta = p2.mom().p3().unit().dot(axis);
              if (abs(p.pid())==3322)      _h[_sqs+"xi"]->fill(ctheta);
              else if (abs(p.pid())==3214) _h[_sqs+"sig"]->fill(ctheta);
              break;
            }
          }
        }
        if (matched) break;
      }
    }

    pair<double,pair<double,double> > calcAlpha(const Histo1DPtr& hist) const {
      if (hist->numEntries()==0.) return make_pair(0.,make_pair(0.,0.));
      double d = 3./(pow(hist->xMax(),3)-pow(hist->xMin(),3));
      double c = 3.*(hist->xMax()-hist->xMin())/(pow(hist->xMax(),3)-pow(hist->xMin(),3));
      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 =  d*(bin.xMax() - bin.xMin());
        double b = d/3.*(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 = (-c*sum1 + sqr(c)*sum2 + sum3 - c*sum5)/(sum1 - c*sum2 + c*sum4 - sum5);
      // and error
      double cc = -pow((sum3 + sqr(c)*sum4 - 2*c*sum5),3);
      double bb = -2*sqr(sum3 + sqr(c)*sum4 - 2*c*sum5)*(sum1 - c*sum2 + c*sum4 - sum5);
      double aa =  sqr(sum1 - c*sum2 + c*sum4 - sum5)*(-sum3 - sqr(c)*sum4 + sqr(sum1 - c*sum2 + c*sum4 - sum5) + 2*c*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() {

      normalize(_h, 1.0, false);

      size_t ih = 0;
      Estimate0DPtr est;
      pair<double,pair<double,double> > alpha;
      for (double eVal : allowedEnergies()) {

        const string en = toString(round(eVal/MeV));
        if (isCompatibleWithSqrtS(eVal, 1e-1))  _sqs = en;

        book(est, 2, 1+ih, 1);
        alpha = calcAlpha(_h[en+"sig"]);
        est->set(alpha.first, alpha.second);

        book(est, 2, 2+ih, 1);
        alpha = calcAlpha(_h[en+"xi"]);
        est->set(alpha.first, alpha.second);
        ih += 2;
      }
    }
    /// @}

    /// @name Histograms
    /// @{
    map<string,Histo1DPtr> _h;
    string _sqs = "";
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2017_I1506414);


}