rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

KLOE2_2016_I1416990

Measurement of the Dalitz plot for $\eta\to\pi^+\pi^-\pi^0$
Experiment: KLOE2 (DAPHNE)
Inspire ID: 1416990
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • JHEP 1605 (2016) 019
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing eta mesons

Measurement of the dalitz plot for the decay $\eta\to\pi^+\pi^-\pi^0$ by the KLOE2 collaboration. The distributions are normalised such that the bin at $X=0$, $Y=0.05$ is $1$.

Source code: KLOE2_2016_I1416990.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief eta -> 3 pi analysis
  9  class KLOE2_2016_I1416990 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(KLOE2_2016_I1416990);
 14
 15
 16    /// @name Analysis methods
 17    //@{
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21      // Initialise and register projections
 22      declare(UnstableParticles(), "UFS");
 23
 24      // Book histograms
 25      book(_dalitz, 1,1,1);
 26      double step(0.1), x(-0.9);
 27      for(unsigned int ix=1;ix<18;++ix) {
 28	Histo1DPtr temp;
 29	book(temp,2,1,ix);
 30	_h_dalitz.add( x, x+step, temp);
 31	x += step;
 32      }
 33      book(_norm,"TMP/norm");
 34    }
 35    
 36    void findDecayProducts(const Particle & mother, unsigned int & nstable,
 37			   Particles &pi0, Particles &pip, Particles &pim) {
 38      for(const Particle & p : mother.children()) {
 39        int id = p.pid();
 40        if (id == PID::PIMINUS ) {
 41	  pim.push_back(p);
 42          ++nstable;
 43	}
 44        else if (id == PID::PIPLUS) {
 45	  pip.push_back(p);
 46          ++nstable;
 47        }
 48        else if (id == PID::PI0) {
 49	  pi0.push_back(p);
 50          ++nstable;
 51        }
 52        else if ( !p.children().empty() ) {
 53          findDecayProducts(p, nstable, pi0,pip,pim);
 54        }
 55        else
 56          ++nstable;
 57      }
 58    }
 59
 60    /// Perform the per-event analysis
 61    void analyze(const Event& event) {
 62      // Loop over eta mesons
 63      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==PID::ETA)) {
 64      	Particles pi0, pip, pim;
 65      	unsigned nstable(0);
 66      	findDecayProducts(p,nstable,pi0,pip,pim);
 67      	if(nstable==3 && pi0.size()==1 && pip.size()==1 && pim.size()==1) {
 68	  // massesx
 69      	  double meta = p.mass();
 70      	  double mpip = pip[0].mass();
 71      	  double mpim = pim[0].mass();
 72      	  double mpi0 = pi0[0].mass();
 73	  // kinetic energies
 74      	  double Q  = meta-mpip-mpim-mpi0;
 75      	  double Ep = 0.5/meta*(sqr(meta)+sqr(mpip)-(p.momentum()-pip[0].momentum()).mass2())-mpip;
 76      	  double Em = 0.5/meta*(sqr(meta)+sqr(mpim)-(p.momentum()-pim[0].momentum()).mass2())-mpim;
 77      	  double E0 = 0.5/meta*(sqr(meta)+sqr(mpi0)-(p.momentum()-pi0[0].momentum()).mass2())-mpi0;
 78	  // X and Y variables
 79      	  double X = sqrt(3.)/Q*(Ep-Em);
 80      	  double Y = 3.*E0/Q-1.;
 81       	  _dalitz ->fill(X,Y);
 82	  _h_dalitz.fill(Y,X);
 83       	  if(fabs(X)<0.03225806451612903 && Y>0. && Y<0.1) _norm->fill();
 84      	}
 85      }
 86    }
 87
 88
 89    /// Normalise histograms etc., after the run
 90    void finalize() {
 91      scale(_dalitz,0.06451612903225806*0.1/ *_norm);
 92      for (Histo1DPtr histo : _h_dalitz.histos()) scale(histo,0.06451612903225806/ *_norm);
 93
 94    }
 95
 96    //@}
 97
 98
 99    /// @name Histograms
100    //@{
101    Histo2DPtr _dalitz;
102    BinnedHistogram _h_dalitz;
103    CounterPtr _norm;
104    //@}
105
106
107  };
108
109
110  // The hook for the plugin system
111  RIVET_DECLARE_PLUGIN(KLOE2_2016_I1416990);
112
113
114}