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 J/psi and psi(2s) -> Xi* and Sigma*
 11  class BESIII_2017_I1506414 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1506414);
 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      if(isCompatibleWithSqrtS(3.1*GeV,1e-1)) {
 31        book(_h_xi , 1, 1, 2);
 32        book(_h_sig, 1, 1, 1);
 33      }
 34      else if (isCompatibleWithSqrtS(3.686*GeV, 1E-1)) {
 35        book(_h_xi , 1, 1, 4);
 36        book(_h_sig, 1, 1, 3);
 37      }
 38    }
 39
 40    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 41      for( const Particle &child : p.children()) {
 42        if(child.children().empty()) {
 43          nRes[child.pid()]-=1;
 44          --ncount;
 45        }
 46        else
 47          findChildren(child,nRes,ncount);
 48      }
 49    }
 50
 51    /// Perform the per-event analysis
 52    void analyze(const Event& event) {
 53      // get the axis, direction of incoming electron
 54      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 55      Vector3 axis;
 56      if(beams.first.pid()>0)
 57        axis = beams.first .momentum().p3().unit();
 58      else
 59        axis = beams.second.momentum().p3().unit();
 60      // types of final state particles
 61      const FinalState& fs = apply<FinalState>(event, "FS");
 62      map<long,int> nCount;
 63      int ntotal(0);
 64      for (const Particle& p :  fs.particles()) {
 65        nCount[p.pid()] += 1;
 66        ++ntotal;
 67      }
 68
 69
 70      const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
 71      for (const Particle& p :  ufs.particles(Cuts::abspid==3322 or
 72					      Cuts::abspid==3214)) {
 73       	if(p.children().empty()) continue;
 74       	map<long,int> nRes=nCount;
 75       	int ncount = ntotal;
 76       	findChildren(p,nRes,ncount);
 77        bool matched=false;
 78        // check for antiparticle
 79        for (const Particle& p2 :  ufs.particles(Cuts::pid==-p.pid())) {
 80          if(p2.children().empty()) continue;
 81          map<long,int> nRes2=nRes;
 82          int ncount2 = ncount;
 83          findChildren(p2,nRes2,ncount2);
 84          if(ncount2==0) {
 85            matched = true;
 86            for(auto const & val : nRes2) {
 87              if(val.second!=0) {
 88                matched = false;
 89                break;
 90              }
 91            }
 92            // found baryon and antibaryon
 93            if(matched) {
 94              // calc cosine
 95              double ctheta;
 96              if(p.pid()>0)
 97                ctheta = p .momentum().p3().unit().dot(axis);
 98              else
 99                ctheta = p2.momentum().p3().unit().dot(axis);
100              if(abs(p.pid())==3322)
101                _h_xi ->fill(ctheta);
102              else if(abs(p.pid())==3214)
103                _h_sig->fill(ctheta);
104              break;
105            }
106          }
107        }
108        if(matched) break;
109      }
110    }
111
112    pair<double,pair<double,double> > calcAlpha(Histo1DPtr hist) {
113      if(hist->numEntries()==0.) return make_pair(0.,make_pair(0.,0.));
114      double d = 3./(pow(hist->xMax(),3)-pow(hist->xMin(),3));
115      double c = 3.*(hist->xMax()-hist->xMin())/(pow(hist->xMax(),3)-pow(hist->xMin(),3));
116      double sum1(0.),sum2(0.),sum3(0.),sum4(0.),sum5(0.);
117      for (const auto& bin : hist->bins() ) {
118        double Oi = bin.sumW();
119        if(Oi==0.) continue;
120        double a =  d*(bin.xMax() - bin.xMin());
121        double b = d/3.*(pow(bin.xMax(),3) - pow(bin.xMin(),3));
122        double Ei = bin.errW();
123        sum1 +=   a*Oi/sqr(Ei);
124        sum2 +=   b*Oi/sqr(Ei);
125        sum3 += sqr(a)/sqr(Ei);
126        sum4 += sqr(b)/sqr(Ei);
127        sum5 +=    a*b/sqr(Ei);
128      }
129      // calculate alpha
130      double alpha = (-c*sum1 + sqr(c)*sum2 + sum3 - c*sum5)/(sum1 - c*sum2 + c*sum4 - sum5);
131      // and error
132      double cc = -pow((sum3 + sqr(c)*sum4 - 2*c*sum5),3);
133      double bb = -2*sqr(sum3 + sqr(c)*sum4 - 2*c*sum5)*(sum1 - c*sum2 + c*sum4 - sum5);
134      double aa =  sqr(sum1 - c*sum2 + c*sum4 - sum5)*(-sum3 - sqr(c)*sum4 + sqr(sum1 - c*sum2 + c*sum4 - sum5) + 2*c*sum5);
135      double dis = sqr(bb)-4.*aa*cc;
136      if(dis>0.) {
137        dis = sqrt(dis);
138        return make_pair(alpha,make_pair(0.5*(-bb+dis)/aa,-0.5*(-bb-dis)/aa));
139      }
140      else {
141        return make_pair(alpha,make_pair(0.,0.));
142      }
143    }
144
145    /// Normalise histograms etc., after the run
146    void finalize() {
147      // find energy
148      int ioff=-1;
149      if(isCompatibleWithSqrtS(3.1*GeV,1e-1)) ioff=0;
150      else if (isCompatibleWithSqrtS(3.686*GeV, 1E-1)) ioff=1;
151      normalize(_h_xi,1.,false);
152      Estimate0DPtr _h_alpha_xi;
153      book(_h_alpha_xi,2,2*ioff+2,1);
154      pair<double,pair<double,double> > alpha = calcAlpha(_h_xi);
155      _h_alpha_xi->set(alpha.first, make_pair(alpha.second.first,alpha.second.second));
156      normalize(_h_sig,1.,false);
157      Estimate0DPtr _h_alpha_sig;
158      book(_h_alpha_sig,2,2*ioff+1,1);
159      alpha = calcAlpha(_h_sig);
160      _h_alpha_sig->set(alpha.first, make_pair(alpha.second.first,alpha.second.second));
161
162    }
163    /// @}
164
165    /// @name Histograms
166    /// @{
167    Histo1DPtr _h_xi,_h_sig;
168    /// @}
169
170
171  };
172
173
174  RIVET_DECLARE_PLUGIN(BESIII_2017_I1506414);
175
176
177}