Rivet analyses referenceBESIII_2015_I1376484Kinematic 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:
Beam energies: ANY Run details:
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}
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