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BESIII_2015_I1376484

Kinematic distributions in the decay $\eta\to\pi^+\pi^-\pi^0$ and $\eta^{(\prime)}\to\pi^0\pi^0\pi^0$
Experiment: BESIII (BEPC)
Inspire ID: 1376484
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 92 (2015) 012014
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing eta/etaprime mesons

Measurement of kinematic distributions in the decays $\eta\to\pi^+\pi^-\pi^0$ and $\eta^{(\prime)}\to\pi^0\pi^0\pi^0$. The data was read from the plots in the paper and the backgrounds subtract in the $\eta^\prime$ decays.

Source code: BESIII_2015_I1376484.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4#include "Rivet/Projections/DecayedParticles.hh"
 5
 6namespace Rivet {
 7
 8
 9  /// @brief eta -> pi+pi-pi0 and eta' -> pi0pi0pi0$
10  class BESIII_2015_I1376484 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1376484);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      // Initialise and register projections
23      UnstableParticles ufs = UnstableParticles(Cuts::pid==PID::ETA or
24						Cuts::pid==PID::ETAPRIME);
25      declare(ufs, "UFS");
26      DecayedParticles ETA(ufs);
27      ETA.addStable(PID::PI0);
28      ETA.addStable(PID::K0S);
29      ETA.addStable(PID::ETA);
30      declare(ETA, "ETA");
31      for(unsigned int ix=0;ix<2;++ix) {
32	book(_h[ix  ],1,1,1+ix);
33	book(_h[ix+2],2+ix,1,1);
34      }
35    }
36
37
38    /// Perform the per-event analysis
39    void analyze(const Event& event) {
40      static const map<PdgId,unsigned int> & mode1  = { {211,1}, {-211,1}, {111,1} };
41      static const map<PdgId,unsigned int> & mode2   = { {111,3} };
42      DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
43      // loop over particles
44      for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
45	// select right decay mode
46	if ( ETA.decaying()[ix].pid()==PID::ETA && ETA.modeMatches(ix,3,mode1)) {
47	  const Particle & pi0 = ETA.decayProducts()[ix].at( 111)[0];
48	  const Particle & pip = ETA.decayProducts()[ix].at( 211)[0];
49	  const Particle & pim = ETA.decayProducts()[ix].at(-211)[0];
50	  double s1 = (pi0.momentum()+pim.momentum()).mass2();
51	  double s2 = (pi0.momentum()+pip.momentum()).mass2();
52	  double s3 = (pip.momentum()+pim.momentum()).mass2();
53	  double mOut = pi0.mass()+pip.mass()+pim.mass();
54	  double Q = ETA.decaying()[ix].mass()-mOut;
55	  double X = sqrt(3.)/2./ETA.decaying()[ix].mass()/Q*(s1-s2);
56	  double Y = 3.*(sqr(ETA.decaying()[ix].mass()-pi0.mass())-s3)/2./ETA.decaying()[ix].mass()/Q-1.;
57	  _h[0]->fill(X);
58	  _h[1]->fill(Y);
59	}
60	else if  ( ETA.modeMatches(ix,3,mode2)) {
61	  const Particles & pi0 = ETA.decayProducts()[ix].at(111);
62	  double s1 = (pi0[2].momentum()+pi0[1].momentum()).mass2();
63	  double s2 = (pi0[2].momentum()+pi0[0].momentum()).mass2();
64	  double s3 = (pi0[0].momentum()+pi0[1].momentum()).mass2();
65	  double mOut = pi0[2].mass()+pi0[0].mass()+pi0[1].mass();
66	  double Q = ETA.decaying()[ix].mass()-mOut;
67	  double X = sqrt(3.)/2./ETA.decaying()[ix].mass()/Q*(s1-s2);
68	  double Y = 3.*(sqr(ETA.decaying()[ix].mass()-pi0[2].mass())-s3)/2./ETA.decaying()[ix].mass()/Q-1.;
69	  double Z = sqr(X)+sqr(Y);
70	  if(ETA.decaying()[ix].pid()==PID::ETA) _h[2]->fill(Z);
71	  else _h[3]->fill(Z);
72	}
73      }
74    }
75
76
77    /// Normalise histograms etc., after the run
78    void finalize() {
79      for(unsigned int ix=0;ix<4;++ix)
80	normalize(_h[ix]);
81    }
82
83    /// @}
84
85
86    /// @name Histograms
87    /// @{
88    Histo1DPtr _h[4];
89    /// @}
90
91
92  };
93
94
95  RIVET_DECLARE_PLUGIN(BESIII_2015_I1376484);
96
97}