rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

BABAR_2018_I1647139

Cross section for $e^+e^-\to\eta\pi^+\pi^-$ between 1.2 and 3.5 GeV
Experiment: BABAR (PEP-II)
Inspire ID: 1647139
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D97 (2018) 052007
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e- to hadrons

Measurement of the cross section for $e^+e^-\to\eta\pi^+\pi^-$ at energies between 1.2 and 3.5 GeV using radiative events.

Source code: BABAR_2018_I1647139.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief Add a short analysis description here
 10  class BABAR_2018_I1647139 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2018_I1647139);
 15
 16
 17    /// @name Analysis methods
 18    //@{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22
 23      // Initialise and register projections
 24      declare(FinalState(), "FS");
 25      declare(UnstableParticles(), "UFS");
 26      book(_numEtaPiPi, "TMP/EtaPiPi");
 27
 28    }
 29
 30
 31    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 32      for (const Particle &child : p.children()) {
 33	if(child.children().empty()) {
 34	  --nRes[child.pid()];
 35	  --ncount;
 36	}
 37	else
 38	  findChildren(child,nRes,ncount);
 39      }
 40    }
 41
 42    /// Perform the per-event analysis
 43    void analyze(const Event& event) {
 44      const FinalState& fs = apply<FinalState>(event, "FS");
 45
 46      map<long,int> nCount;
 47      int ntotal(0);
 48      for (const Particle& p : fs.particles()) {
 49	nCount[p.pid()] += 1;
 50	++ntotal;
 51      }
 52      const FinalState& ufs = apply<FinalState>(event, "UFS");
 53      for (const Particle& p : ufs.particles()) {
 54	if(p.children().empty()) continue;
 55	// find the omega
 56	if(p.pid()==221) {
 57	  map<long,int> nRes = nCount;
 58	  int ncount = ntotal;
 59	  findChildren(p,nRes,ncount);
 60	  // eta pi+pi-
 61	  if(ncount!=2) continue;
 62	  bool matched = true;
 63	  for(auto const & val : nRes) {
 64	    if(abs(val.first)==211) {
 65	      if(val.second !=1) {
 66		matched = false;
 67		break;
 68	      }
 69	    }
 70	    else if(val.second!=0) {
 71	      matched = false;
 72	      break;
 73	    }
 74	  }
 75	  if(matched)
 76	    _numEtaPiPi->fill();
 77	}
 78      }
 79    }
 80
 81
 82    /// Normalise histograms etc., after the run
 83    void finalize() {
 84
 85      double sigma = _numEtaPiPi->val();
 86      double error = _numEtaPiPi->err();
 87      sigma *= crossSection()/ sumOfWeights() /nanobarn;
 88      error *= crossSection()/ sumOfWeights() /nanobarn; 
 89      Scatter2D temphisto(refData(1, 1, 1));
 90      Scatter2DPtr  mult;
 91      book(mult, 1, 1, 1);
 92      for (size_t b = 0; b < temphisto.numPoints(); b++) {
 93	const double x  = temphisto.point(b).x();
 94	pair<double,double> ex = temphisto.point(b).xErrs();
 95	pair<double,double> ex2 = ex;
 96	if(ex2.first ==0.) ex2. first=0.0001;
 97	if(ex2.second==0.) ex2.second=0.0001;
 98	if (inRange(sqrtS()/GeV, x-ex2.first, x+ex2.second)) {
 99	  mult->addPoint(x, sigma, ex, make_pair(error,error));
100	}
101	else {
102	  mult->addPoint(x, 0., ex, make_pair(0.,.0));
103	}
104      }
105    }
106
107    //@}
108
109
110    /// @name Histograms
111    //@{
112    CounterPtr _numEtaPiPi;
113    //@}
114
115
116  };
117
118
119  // The hook for the plugin system
120  RIVET_DECLARE_PLUGIN(BABAR_2018_I1647139);
121
122
123}