1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/Beam.hh"
  4#include "Rivet/Projections/FinalState.hh"
  5#include "Rivet/Projections/UnstableParticles.hh"
  6
  7namespace Rivet {
  8
  9
 10  /// @brief BES psi2s -> Xi*- Xibar+ + c.c.
 11  class BESIII_2019_I1765606 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1765606);
 16
 17
 18    /// @name Analysis methods
 19    /// @{
 20
 21    /// Book histograms and initialise projections before the run
 22    void init() {
 23
 24      // Initialise and register projections
 25      declare(Beam(), "Beams");
 26      declare(UnstableParticles(), "UFS");
 27      declare(FinalState(), "FS");
 28
 29      // Book histograms
 30      book(_h_cTheta, 1, 1, 1);
 31
 32    }
 33
 34    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 35      for(const Particle &child : p.children()) {
 36        if(child.children().empty()) {
 37          nRes[child.pid()]-=1;
 38          --ncount;
 39        }
 40        else
 41          findChildren(child,nRes,ncount);
 42      }
 43    }
 44
 45    /// Perform the per-event analysis
 46    void analyze(const Event& event) {
 47      // get the axis, direction of incoming electron
 48      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 49      Vector3 axis;
 50      if(beams.first.pid()<0)
 51        axis = beams.first .momentum().p3().unit();
 52      else
 53        axis = beams.second.momentum().p3().unit();
 54      // types of final state particles
 55      const FinalState& fs = apply<FinalState>(event, "FS");
 56      map<long,int> nCount;
 57      int ntotal(0);
 58      for (const Particle& p : fs.particles()) {
 59        nCount[p.pid()] += 1;
 60        ++ntotal;
 61      }
 62      const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
 63      for (const Particle& p : ufs.particles(Cuts::abspid==3314)) {
 64        if(p.children().empty()) continue;
 65        map<long,int> nRes=nCount;
 66        int ncount = ntotal;
 67        findChildren(p,nRes,ncount);
 68        bool matched=false;
 69        int sign = p.pid()/3314;
 70        for (const Particle& p2 : ufs.particles(Cuts::pid==-sign*3312)) {
 71          if(p2.children().empty()) continue;
 72          map<long,int> nRes2=nRes;
 73          int ncount2 = ncount;
 74          findChildren(p2,nRes2,ncount2);
 75          if(ncount2==0) {
 76            matched = true;
 77            for(auto const & val : nRes2) {
 78              if(val.second!=0) {
 79                matched = false;
 80                break;
 81              }
 82            }
 83            // fond baryon and antibaryon
 84            if(matched) {
 85              // calc cosine
 86              double cTheta= (sign>0) ? p .momentum().p3().unit().dot(axis) : p2.momentum().p3().unit().dot(axis);
 87              _h_cTheta->fill(cTheta);
 88              break;
 89            }
 90
 91          }
 92        }
 93      }
 94    }
 95
 96    pair<double,pair<double,double> > calcAlpha(Histo1DPtr hist) {
 97      if(hist->numEntries()==0.) return make_pair(0.,make_pair(0.,0.));
 98      double d = 3./(pow(hist->xMax(),3)-pow(hist->xMin(),3));
 99      double c = 3.*(hist->xMax()-hist->xMin())/(pow(hist->xMax(),3)-pow(hist->xMin(),3));
100      double sum1(0.),sum2(0.),sum3(0.),sum4(0.),sum5(0.);
101      for (const auto& bin : hist->bins() ) {
102        double Oi = bin.sumW();
103        if(Oi==0.) continue;
104        double a =  d*(bin.xMax() - bin.xMin());
105        double b = d/3.*(pow(bin.xMax(),3) - pow(bin.xMin(),3));
106        double Ei = bin.errW();
107        sum1 +=   a*Oi/sqr(Ei);
108        sum2 +=   b*Oi/sqr(Ei);
109        sum3 += sqr(a)/sqr(Ei);
110        sum4 += sqr(b)/sqr(Ei);
111        sum5 +=    a*b/sqr(Ei);
112      }
113      // calculate alpha
114      double alpha = (-c*sum1 + sqr(c)*sum2 + sum3 - c*sum5)/(sum1 - c*sum2 + c*sum4 - sum5);
115      // and error
116      double cc = -pow((sum3 + sqr(c)*sum4 - 2*c*sum5),3);
117      double bb = -2*sqr(sum3 + sqr(c)*sum4 - 2*c*sum5)*(sum1 - c*sum2 + c*sum4 - sum5);
118      double aa =  sqr(sum1 - c*sum2 + c*sum4 - sum5)*(-sum3 - sqr(c)*sum4 + sqr(sum1 - c*sum2 + c*sum4 - sum5) + 2*c*sum5);
119      double dis = sqr(bb)-4.*aa*cc;
120      if(dis>0.) {
121        dis = sqrt(dis);
122        return make_pair(alpha,make_pair(0.5*(-bb+dis)/aa,-0.5*(-bb-dis)/aa));
123      }
124      else {
125        return make_pair(alpha,make_pair(0.,0.));
126      }
127    }
128
129    /// Normalise histograms etc., after the run
130    void finalize() {
131      normalize(_h_cTheta);
132      Estimate0DPtr h_alpha_xi;
133      book(h_alpha_xi,2,1,1);
134      pair<double,pair<double,double> > alpha = calcAlpha(_h_cTheta);
135      h_alpha_xi->set(alpha.first, alpha.second);
136    }
137
138    /// @}
139
140
141    /// @name Histograms
142    /// @{
143    Histo1DPtr _h_cTheta;
144    /// @}
145
146  };
147
148
149  RIVET_DECLARE_PLUGIN(BESIII_2019_I1765606);
150
151}