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 psi2s -> Xi*0 Xibar*0
 11  class BESIII_2021_I1921775 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1921775);
 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(_h_xi , 1, 1, 1);
 30      book(_h_xiB, 1, 1, 2);
 31    }
 32
 33    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 34      for(const Particle &child : p.children()) {
 35	if(child.children().empty()) {
 36	  nRes[child.pid()]-=1;
 37	  --ncount;
 38	}
 39	else
 40	  findChildren(child,nRes,ncount);
 41      }
 42    }
 43
 44    /// Perform the per-event analysis
 45    void analyze(const Event& event) {
 46      // get the axis, direction of incoming electron
 47      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 48      Vector3 axis;
 49      if(beams.first.pid()>0)
 50	axis = beams.first .momentum().p3().unit();
 51      else
 52	axis = beams.second.momentum().p3().unit();
 53      // types of final state particles
 54      const FinalState& fs = apply<FinalState>(event, "FS");
 55      map<long,int> nCount;
 56      int ntotal(0);
 57      for (const Particle& p : fs.particles()) {
 58	nCount[p.pid()] += 1;
 59	++ntotal;
 60      }
 61
 62      const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
 63      for (const Particle& p : ufs.particles(Cuts::abspid==3324)) {
 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	// check for antiparticle
 70	for (const Particle& p2 : ufs.particles(Cuts::pid==-p.pid())) {
 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 ctheta1 = p .momentum().p3().unit().dot(axis);
 87	      double ctheta2 = p2.momentum().p3().unit().dot(axis);
 88	      if(p.pid()<0) swap(ctheta1,ctheta2);
 89	      _h_xi->fill(ctheta1);
 90	      _h_xiB->fill(ctheta2);
 91	      break;
 92	    }
 93	  }
 94	}
 95	if(matched) break;
 96      }
 97    }
 98
 99    pair<double,pair<double,double> > calcAlpha(Histo1DPtr hist) {
100      if(hist->numEntries()==0.) return make_pair(0.,make_pair(0.,0.));
101      double d = 3./(pow(hist->xMax(),3)-pow(hist->xMin(),3));
102      double c = 3.*(hist->xMax()-hist->xMin())/(pow(hist->xMax(),3)-pow(hist->xMin(),3));
103      double sum1(0.),sum2(0.),sum3(0.),sum4(0.),sum5(0.);
104      for (const auto& bin : hist->bins() ) {
105       	double Oi = bin.sumW();
106        if(Oi==0.) continue;
107        double a =  d*(bin.xMax() - bin.xMin());
108        double b = d/3.*(pow(bin.xMax(),3) - pow(bin.xMin(),3));
109       	double Ei = bin.errW();
110        sum1 +=   a*Oi/sqr(Ei);
111        sum2 +=   b*Oi/sqr(Ei);
112        sum3 += sqr(a)/sqr(Ei);
113        sum4 += sqr(b)/sqr(Ei);
114        sum5 +=    a*b/sqr(Ei);
115      }
116      // calculate alpha
117      double alpha = (-c*sum1 + sqr(c)*sum2 + sum3 - c*sum5)/(sum1 - c*sum2 + c*sum4 - sum5);
118      // and error
119      double cc = -pow((sum3 + sqr(c)*sum4 - 2*c*sum5),3);
120      double bb = -2*sqr(sum3 + sqr(c)*sum4 - 2*c*sum5)*(sum1 - c*sum2 + c*sum4 - sum5);
121      double aa =  sqr(sum1 - c*sum2 + c*sum4 - sum5)*(-sum3 - sqr(c)*sum4 + sqr(sum1 - c*sum2 + c*sum4 - sum5) + 2*c*sum5);
122      double dis = sqr(bb)-4.*aa*cc;
123      if(dis>0.) {
124        dis = sqrt(dis);
125        return make_pair(alpha,make_pair(0.5*(-bb+dis)/aa,-0.5*(-bb-dis)/aa));
126      }
127      else {
128        return make_pair(alpha,make_pair(0.,0.));
129      }
130    }
131
132    /// Normalise histograms etc., after the run
133    void finalize() {
134      normalize(_h_xi ,1.,false);
135      normalize(_h_xiB,1.,false);
136      Estimate1DPtr _h_alpha_xi;
137      book(_h_alpha_xi, 2,1,1);
138      pair<double,pair<double,double> > alpha = calcAlpha(_h_xi);
139      _h_alpha_xi->bin(1).set(alpha.first, make_pair(alpha.second.first,alpha.second.second));
140    }
141
142    /// @}
143
144
145    /// @name Histograms
146    /// @{
147    Histo1DPtr _h_xi,_h_xiB;
148    /// @}
149
150
151  };
152
153
154  RIVET_DECLARE_PLUGIN(BESIII_2021_I1921775);
155
156}