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BABAR_2021_I1937349

Cross section for $e^+e^-\to$ $\pi^+\pi^-\pi^0$ between 0.62 and 3.5 GeV
Experiment: BABAR (PEP-II)
Inspire ID: 1937349
Status: VALIDATED
Authors:
  • Peter Richardson
References: Beams: e+ e-
Beam energies: ANY
    No run details listed

Measurement of the cross section for $e^+e^-\to \pi^+\pi^-\pi^0$ by BaBar using radiative return for energies between 0.62 and 3.5 GeV. The contribution of the $J/\psi$ has been subtracted.

Source code: BABAR_2021_I1937349.cc 
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"

namespace Rivet {


  /// @brief e+e- -> pi+pi-pi0
  class BABAR_2021_I1937349 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2021_I1937349);


    /// @name Analysis methods
    ///@{

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(FinalState(), "FS");

      book(_num3pi, "TMP/num3");
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& fs = apply<FinalState>(event, "FS");

      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
	nCount[p.pid()] += 1;
	++ntotal;
      }
      if(ntotal!=3) vetoEvent;
      if(nCount[-211]==1&&nCount[211]==1&&nCount[111]==1)
	_num3pi->fill();
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double sigma = _num3pi->val();
      double error = _num3pi->err();
      sigma *= crossSection()/ sumOfWeights() /nanobarn;
      error *= crossSection()/ sumOfWeights() /nanobarn;
      Scatter2D temphisto(refData(1, 1, 1));
      Scatter2DPtr  mult;
      book(mult, 1, 1, 1);
      for (size_t b = 0; b < temphisto.numPoints(); b++) {
	const double x  = temphisto.point(b).x();
	pair<double,double> ex = temphisto.point(b).xErrs();
	pair<double,double> ex2 = ex;
	if(ex2.first ==0.) ex2. first=0.0001;
	if(ex2.second==0.) ex2.second=0.0001;
	if (inRange(sqrtS()/GeV, x-ex2.first, x+ex2.second)) {
	  mult->addPoint(x, sigma, ex, make_pair(error,error));
	}
	else {
	  mult->addPoint(x, 0., ex, make_pair(0.,.0));
	}
      }
    }

    ///@}


    /// @name Histograms
    ///@{
    CounterPtr _num3pi;
    ///@}


  };


  RIVET_DECLARE_PLUGIN(BABAR_2021_I1937349);

}