Rivet analyses referenceBESIII_2018_I1703033Dalitz plot analysis of $\omega\to\pi^+\pi^-\pi^0$Experiment: BESIII (BEPC) Inspire ID: 1703033 Status: VALIDATED NOHEPDATA Authors:
Beam energies: ANY Run details:
Measurement of kinematic distributions in the decay $\omega\to\pi^+\pi^-\pi^0$ by BESIII. The data were read from the plots in the paper and therefore for most points the error bars are the size of the point. It is also not clear that any resolution/acceptance effects have been unfolded. Source code: BESIII_2018_I1703033.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 omega -> pi+pi-pi0
10 class BESIII_2018_I1703033 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1703033);
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== 223);
24 declare(ufs, "UFS");
25 DecayedParticles OMEGA(ufs);
26 OMEGA.addStable(PID::PI0);
27 declare(OMEGA,"OMEGA");
28 // histograms
29 book(_h_z ,1,1,1);
30 book(_h_phi,1,1,2);
31 book(_h_cos,1,1,3);
32 book(_h_ppi,1,1,4);
33 book(_dalitz,"dalitz",50,-1,1,50,-1.1,0.9);
34 }
35
36 /// Perform the per-event analysis
37 void analyze(const Event& event) {
38 static const map<PdgId,unsigned int> & mode = { { 211,1}, {-211,1}, { 111,1}};
39 static const std::complex<double> ii(0.,1.);
40 DecayedParticles OMEGA = apply<DecayedParticles>(event, "OMEGA");
41 // loop over particles
42 for(unsigned int ix=0;ix<OMEGA.decaying().size();++ix) {
43 // pi+ pi- pi0
44 if (!OMEGA.modeMatches(ix,3,mode)) continue;
45 // apply omega mass cut
46 if(abs(OMEGA.decaying()[ix].mass()-0.78265)>0.04) continue;
47 // decay products
48 const Particle & pip = OMEGA.decayProducts()[ix].at( 211)[0];
49 const Particle & pim = OMEGA.decayProducts()[ix].at(-211)[0];
50 const Particle & pi0 = OMEGA.decayProducts()[ix].at( 111)[0];
51 LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(OMEGA.decaying()[ix].momentum().betaVec());
52 FourMomentum pp = boost.transform(pip.momentum());
53 FourMomentum pm = boost.transform(pim.momentum());
54 FourMomentum p0 = boost.transform(pi0.momentum());
55 // variables from eqn 1 in paper (use version from Eqn 2.1 of 1010.3946)
56 double Qc = OMEGA.decaying()[ix].mass()-pi0.mass()-pim.mass()-pip.mass();
57 double x = sqrt(3.)*(pm.E()-pp.E())/Qc;
58 double y = 3./Qc*(p0.E()-pi0.mass())-1.;
59 _dalitz->fill(x,y);
60 // plot arg and phase of variable
61 std::complex<double> zz = x+ii*y;
62 _h_z->fill(norm(zz));
63 double phi = arg(zz);
64 if(phi<0.) phi+=2.*M_PI;
65 _h_phi->fill(phi);
66 double ctheta = -pp.p3().unit().dot(p0.p3().unit());
67 _h_cos->fill(ctheta);
68 _h_ppi->fill(p0.p3().mod());
69 }
70 }
71
72
73 /// Normalise histograms etc., after the run
74 void finalize() {
75 normalize(_h_z );
76 normalize(_h_phi);
77 normalize(_h_cos);
78 normalize(_h_ppi);
79 normalize(_dalitz);
80 }
81
82 /// @}
83
84
85 /// @name Histograms
86 /// @{
87 Histo1DPtr _h_z,_h_phi,_h_cos,_h_ppi;
88 Histo2DPtr _dalitz;
89 /// @}
90
91
92 };
93
94
95 RIVET_DECLARE_PLUGIN(BESIII_2018_I1703033);
96
97}
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