1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief Xi_c0 -> Xi-pi+ asymmetry
  9  class BELLE_2021_I1851126 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2021_I1851126);
 14
 15
 16    /// @name Analysis methods
 17    ///@{
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21      // Initialise and register projections
 22      declare(UnstableParticles(Cuts::abspid==4132), "UFS" );
 23      // Book histograms
 24      book(_h_c_P,1,1,1);
 25      book(_h_c_M,1,1,2);
 26    }
 27
 28
 29    /// Perform the per-event analysis
 30    void analyze(const Event& event) {
 31      // loop over Xi_c0 baryons
 32      for( const Particle& Xic : apply<UnstableParticles>(event, "UFS").particles()) {
 33	int sign = Xic.pid()/4132;
 34	if(Xic.children().size()!=2) continue;
 35	Particle baryon1,meson1;
 36	if(Xic.children()[0].pid()==sign*3312 && 
 37	   Xic.children()[1].pid()==sign*211) {
 38	  baryon1 = Xic.children()[0];
 39	  meson1  = Xic.children()[1];
 40	}
 41	else if(Xic.children()[1].pid()==sign*3312 && 
 42		Xic.children()[0].pid()==sign*211) {
 43	  baryon1 = Xic.children()[1];
 44	  meson1  = Xic.children()[0];
 45	}
 46	else
 47	  continue;
 48	Particle baryon2,meson2;
 49	if(baryon1.children()[0].pid()== sign*3122 && 
 50	   baryon1.children()[1].pid()==-sign*211) {
 51	  baryon2 = baryon1.children()[0];
 52	  meson2  = baryon1.children()[1];
 53	}
 54	else if(baryon1.children()[1].pid()== sign*3122 && 
 55		baryon1.children()[0].pid()==-sign*211) {
 56	  baryon2 = baryon1.children()[1];
 57	  meson2  = baryon1.children()[0];
 58	}
 59	else
 60	  continue;
 61	// first boost to the Xic rest frame
 62	LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Xic.momentum().betaVec());
 63	FourMomentum pbaryon1 = boost1.transform(baryon1.momentum());
 64	FourMomentum pbaryon2 = boost1.transform(baryon2.momentum());
 65	// to lambda rest frame
 66	LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pbaryon1.betaVec());
 67	Vector3 axis = pbaryon1.p3().unit();
 68	FourMomentum pp = boost2.transform(pbaryon2);
 69	// calculate angle
 70	double cTheta = pp.p3().unit().dot(axis);
 71	if(sign>0)
 72	  _h_c_P->fill(cTheta,1.);
 73	else
 74	  _h_c_M->fill(cTheta,1.);
 75      }
 76    }
 77
 78    pair<double,double> calcAlpha(Histo1DPtr hist) {
 79      if(hist->numEntries()==0.) return make_pair(0.,0.);
 80      double sum1(0.),sum2(0.);
 81      for (const auto& bin : hist->bins() ) {
 82        double Oi = bin.sumW();
 83        if(Oi==0.) continue;
 84        double ai = 0.5*(bin.xMax()-bin.xMin());
 85        double bi = 0.5*ai*(bin.xMax()+bin.xMin());
 86        double Ei = bin.errW();
 87        sum1 += sqr(bi/Ei);
 88        sum2 += bi/sqr(Ei)*(Oi-ai);
 89      }
 90      return make_pair(sum2/sum1,sqrt(1./sum1));
 91    }
 92
 93    /// Normalise histograms etc., after the run
 94    void finalize() {
 95      // first mode
 96      normalize(_h_c_P);
 97      Estimate0DPtr _h_alpha_P;
 98      book(_h_alpha_P,2,1,1);
 99      pair<double,double> alphaP = calcAlpha(_h_c_P);
100      alphaP.first /= -0.401;
101      alphaP.second/= -0.401;
102      _h_alpha_P->set(alphaP.first, alphaP.second);
103      // second mode
104      normalize(_h_c_M);
105      Estimate0DPtr _h_alpha_M;
106      book(_h_alpha_M,2,1,2);
107      pair<double,double> alphaM = calcAlpha(_h_c_M);
108      alphaM.first /= 0.389;
109      alphaM.second/= 0.389;
110      _h_alpha_M->set(alphaM.first, alphaM.second);
111      // average
112      double aver = 0.5*(-alphaP.first+alphaM.first);
113      double err  = 0.5*sqrt(sqr(alphaP.second)+sqr(alphaM.second));
114      Estimate0DPtr _h_alpha_aver;
115      book(_h_alpha_aver,2,1,3);
116      _h_alpha_aver->set(aver, err);
117      // asymetry
118      double asym = (alphaP.first+alphaM.first)/(alphaP.first-alphaM.first);
119      err         = 2./sqr(alphaP.first-alphaM.first)*sqrt(sqr(alphaM.first *alphaP.second)+
120							   sqr(alphaM.second*alphaP.first ));
121      Estimate0DPtr _h_alpha_asym;
122      book(_h_alpha_asym,2,1,4);
123      _h_alpha_asym->set(asym, err);
124    }
125
126    ///@}
127
128
129    /// @name Histograms
130    ///@{
131    Histo1DPtr _h_c_M,_h_c_P;
132    ///@}
133
134
135  };
136
137
138  RIVET_DECLARE_PLUGIN(BELLE_2021_I1851126);
139
140}