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 D_s+ -> pi+ pi0 pi0
10  class BESIII_2021_I1929365 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1929365);
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::abspid==431);
24      declare(ufs, "UFS");
25      DecayedParticles DS(ufs);
26      DS.addStable(PID::PI0);
27      DS.addStable(PID::K0S);
28      declare(DS,"DS");
29      // histos
30      book(_h_pi0pi0,1,1,1);
31      book(_h_pippi0,1,1,2);
32      book(_dalitz, "dalitz",50,0.,3.5,50,0.,3.5);
33    }
34
35    /// Perform the per-event analysis
36    void analyze(const Event& event) {
37      static const map<PdgId,unsigned int> & mode   = { { 211,1},{ 111,2}};
38      static const map<PdgId,unsigned int> & modeCC = { {-211,1},{ 111,2}};
39      DecayedParticles DS = apply<DecayedParticles>(event, "DS");
40      // loop over particles
41      for(unsigned int ix=0;ix<DS.decaying().size();++ix) {
42	int sign = 1;
43	if (DS.decaying()[ix].pid()>0 && DS.modeMatches(ix,3,mode)) {
44	  sign=1;
45	}
46	else if  (DS.decaying()[ix].pid()<0 && DS.modeMatches(ix,3,modeCC)) {
47	  sign=-1;
48	}
49	else
50	  continue;
51	const Particles & pi0 = DS.decayProducts()[ix].at(      111);
52	const Particle  & pip = DS.decayProducts()[ix].at( sign*211)[0];
53	double mp1  = (pip   .momentum() +pi0[0].momentum()).mass2();
54	double mp2  = (pip   .momentum() +pi0[1].momentum()).mass2();
55	double m0   = (pi0[0].momentum() +pi0[1].momentum()).mass();
56	_dalitz ->fill(mp1,mp2);
57	_dalitz ->fill(mp2,mp1);
58	// K_S0 veto
59	if(m0>0.458 && m0<0.520) continue;
60	_h_pippi0->fill(sqrt(mp1));
61	_h_pippi0->fill(sqrt(mp2));
62	_h_pi0pi0->fill(m0 );
63      }
64    }
65
66
67    /// Normalise histograms etc., after the run
68    void finalize() {
69      normalize(_h_pi0pi0);
70      normalize(_h_pippi0);
71      normalize(_dalitz  );
72    }
73
74    /// @}
75
76
77    /// @name Histograms
78    /// @{
79    Histo1DPtr _h_pi0pi0,_h_pippi0;
80    Histo2DPtr _dalitz;
81    /// @}
82
83
84  };
85
86
87  RIVET_DECLARE_PLUGIN(BESIII_2021_I1929365);
88
89}