1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief Xi-> Lambda pi asymmetry
  9  class CLEOII_2000_I533575 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_2000_I533575);
 14
 15
 16    /// @name Analysis methods
 17    /// @{
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21
 22      // Initialise and register projections
 23      declare(UnstableParticles(), "UFS" );
 24
 25      // Book histograms
 26      book(_h_cthetaM, 2,1,1);
 27      book(_h_cthetaP, 2,1,2);
 28    }
 29
 30
 31    /// Perform the per-event analysis
 32    void analyze(const Event& event) {
 33      // loop over Xi- baryons
 34      for (const Particle& Xi : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==3312)) {
 35	int sign = Xi.pid()/3312;
 36	if(Xi.children().size()!=2) continue;
 37	Particle Lambda,pion1;
 38	if(Xi.children()[0].pid()==sign*3122 &&
 39	   Xi.children()[1].pid()==-sign*211) {
 40	  Lambda = Xi.children()[0];
 41	  pion1   = Xi.children()[1];
 42	}
 43	else if(Xi.children()[1].pid()==sign*3122 &&
 44		Xi.children()[0].pid()==-sign*211) {
 45	  Lambda = Xi.children()[1];
 46	  pion1   = Xi.children()[0];
 47	}
 48	else
 49	  continue;
 50	if(Lambda.children().size()!=2) continue;
 51	Particle proton,pion2;
 52	if(Lambda.children()[0].pid()==sign*2212 &&
 53	   Lambda.children()[1].pid()==-sign*211) {
 54	  proton = Lambda.children()[0];
 55	  pion2   = Lambda.children()[1];
 56	}
 57	else if(Lambda.children()[1].pid()==sign*2212 &&
 58		Lambda.children()[0].pid()==-sign*211) {
 59	  proton = Lambda.children()[1];
 60	  pion2   = Lambda.children()[0];
 61	}
 62	else
 63	  continue;
 64	// boost to xi rest frame first
 65	LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Xi.momentum().betaVec());
 66	FourMomentum pLambda = boost1.transform(Lambda.momentum());
 67	FourMomentum pproton = boost1.transform(proton.momentum());
 68	// to lambda rest frame
 69	LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pLambda.betaVec());
 70	Vector3 axis = pLambda.p3().unit();
 71	FourMomentum pp = boost2.transform(pproton);
 72	// calculate angle
 73	double cTheta = pp.p3().unit().dot(axis);
 74	if(sign==1) {
 75	  _h_cthetaM->fill(cTheta);
 76	}
 77	else {
 78	  _h_cthetaP->fill(cTheta);
 79	}
 80      }
 81    }
 82
 83    pair<double,double> calcAlpha(Histo1DPtr hist) {
 84      if(hist->numEntries()==0.) return make_pair(0.,0.);
 85      double sum1(0.),sum2(0.);
 86      for (const auto& bin : hist->bins() ) {
 87        double Oi = bin.sumW();
 88        if(Oi==0.) continue;
 89        double ai = 0.5*(bin.xMax()-bin.xMin());
 90        double bi = 0.5*ai*(bin.xMax()+bin.xMin());
 91        double Ei = bin.errW();
 92        sum1 += sqr(bi/Ei);
 93        sum2 += bi/sqr(Ei)*(Oi-ai);
 94      }
 95      return make_pair(sum2/sum1,sqrt(1./sum1));
 96    }
 97
 98
 99    /// Normalise histograms etc., after the run
100    void finalize() {
101      normalize(_h_cthetaP);
102      normalize(_h_cthetaM);
103      // calculate the values of alpha
104      // xibar+
105      Estimate0DPtr _h_alphaP;
106      book(_h_alphaP, 1,1,2);
107      pair<double,double> alpha = calcAlpha(_h_cthetaP);
108      _h_alphaP->set(alpha.first, alpha.second);
109      // xi-
110      Estimate0DPtr _h_alphaM;
111      book(_h_alphaM, 1,1,1);
112      alpha = calcAlpha(_h_cthetaM);
113      _h_alphaM->set(alpha.first, alpha.second);
114    }
115
116    /// @}
117
118
119    /// @name Histograms
120    /// @{
121    Histo1DPtr _h_cthetaP,_h_cthetaM;
122    /// @}
123
124
125  };
126
127
128  RIVET_DECLARE_PLUGIN(CLEOII_2000_I533575);
129
130}