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FOCUS_2007_I741543

Mass distributions in the decay $D^0\to \pi^+\pi^-\pi^+\pi^-$
Experiment: FOCUS (Fermilab)
Inspire ID: 741543
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 75 (2007) 052003
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing D0 mesons

Measurement of the mass distributions in the decay $D^0\to \pi^+\pi^-\pi^+\pi^-$ and $D^0\to K^+K^-\pi^+\pi^-$ by the FOCUS collaboration. The data were read from the plots in the paper and therefore for some points the error bars are the size of the point. It is also not clear that any resolution effects have been unfolded.

Source code: FOCUS_2007_I741543.cc 
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"

namespace Rivet {


  /// @brief D0 ->  2pi+2pi-
  class FOCUS_2007_I741543 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(FOCUS_2007_I741543);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid==421);
      declare(ufs, "UFS");
      DecayedParticles D0(ufs);
      D0.addStable(PID::PI0);
      D0.addStable(PID::K0S);
      D0.addStable(PID::ETA);
      D0.addStable(PID::ETAPRIME);
      declare(D0, "D0");
      // histograms
      for(unsigned int ix=0;ix<4;++ix)
	book(_h[ix   ],1,1,1+ix);
      book(_h[4],2,1,1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // define the decay mode
      static const map<PdgId,unsigned int> & mode1   = { { 211,2}, { -211,2}};
      DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
      // loop over particles
      for(unsigned int ix=0;ix<D0.decaying().size();++ix) {
	int sign = D0.decaying()[ix].pid()/421;
	if ( D0.modeMatches(ix,4,mode1)) {
	  const Particles & pip= D0.decayProducts()[ix].at( sign*211);
	  const Particles & pim= D0.decayProducts()[ix].at(-sign*211);
	  set<double> mpm; 
	  for(unsigned int ix=0;ix<2;++ix) {
	    for(unsigned int iy=0;iy<2;++iy) {
	      double m = (pip[ix].momentum()+pim[iy].momentum()).mass();
	      _h[0]->fill(m);
	      mpm.insert(m);
	    }
	  }
	  _h[1]->fill(*mpm.rbegin());
	  _h[2]->fill(*mpm.begin());
	  FourMomentum ppp = pip[0].momentum()+pip[1].momentum();
	  _h[3]->fill(ppp.mass());
	  FourMomentum pmm = pim[0].momentum()+pim[1].momentum();
	  _h[3]->fill(pmm.mass());
	  for(unsigned int ix=0;ix<2;++ix) {
	    _h[4]->fill((ppp+pim[ix].momentum()).mass());
	    _h[4]->fill((pmm+pip[ix].momentum()).mass());
	  }
	}
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for(unsigned int ix=0;ix<5;++ix)
	normalize(_h[ix],1.,false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[5];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(FOCUS_2007_I741543);

}