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E791_2001_I530320

Dalitz plot analysis of $D^+\to \pi^+\pi^+\pi^-$
Experiment: E791 (Fermilab)
Inspire ID: 530320
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.Lett. 86 (2001) 770-774
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing D+ -> pi+ pi+ pi-

Measurement of the mass distributions in the decay $D^+\to \pi^+\pi^+\pi^-$. The data were read from the plots in the paper. Resolution/acceptance effects have been not unfolded and given the agreement with the model in the paper this analysis should only be used for qualitative studies.

Source code: E791_2001_I530320.cc 
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"

namespace Rivet {


  /// @brief  D+ -> pi+pi+pi-
  class E791_2001_I530320 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(E791_2001_I530320);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid==411);
      declare(ufs, "UFS");
      DecayedParticles DP(ufs);
      DP.addStable(PID::PI0);
      DP.addStable(PID::K0S);
      declare(DP,"DP");
      // histos
      book(_h_pi,1,1,1);
      book(_dalitz, "dalitz",50,0.,3.1,50,0.0,3.1);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode   = { { 211,2},{-211,1}};
      static const map<PdgId,unsigned int> & modeCC = { {-211,2},{ 211,1}};
      DecayedParticles DP = apply<DecayedParticles>(event, "DP");
      // loop over particles
      for(unsigned int ix=0;ix<DP.decaying().size();++ix) {
	int sign = 1;
	if (DP.decaying()[ix].pid()>0 && DP.modeMatches(ix,3,mode)) {
	  sign=1;
	}
	else if  (DP.decaying()[ix].pid()<0 && DP.modeMatches(ix,3,modeCC)) {
	  sign=-1;
	}
	else
	  continue;
	const Particles & pip = DP.decayProducts()[ix].at( sign*211);
	const Particle  & pim = DP.decayProducts()[ix].at(-sign*211)[0];
	double m1 = (pim.momentum()+pip[0].momentum()).mass2();
	double m2 = (pim.momentum()+pip[1].momentum()).mass2();
	_h_pi->fill(m1);
	_h_pi->fill(m2);
	_dalitz->fill(m1,m2);
	_dalitz->fill(m2,m1);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_pi);
      normalize(_dalitz);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_pi;
    Histo2DPtr _dalitz;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(E791_2001_I530320);

}