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 BS0 -> J/psi f0
10  class LHCB_2013_I1081268 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2013_I1081268);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      // projections
23      UnstableParticles ufs = UnstableParticles(Cuts::abspid==531);
24      declare(ufs, "UFS");
25      DecayedParticles BS0(ufs);
26      BS0.addStable( 443);
27      declare(BS0, "BS0");
28      // histograms
29      for (unsigned int ix=0;ix<2;++ix) {
30        book(_h[ix],1,1,1+ix);
31      }
32    }
33
34
35    /// Perform the per-event analysis
36    void analyze(const Event& event) {
37      DecayedParticles BS0 = apply<DecayedParticles>(event, "BS0");
38      static const map<PdgId,unsigned int> mode = { { 211,1}, {-211,1}, { 443,1}};
39      for (unsigned int ix=0; ix<BS0.decaying().size(); ++ix) {
40       	if (!BS0.modeMatches(ix,3,mode)) continue;
41      	const Particle& pip  = BS0.decayProducts()[ix].at( 211)[0];
42      	const Particle& pim  = BS0.decayProducts()[ix].at(-211)[0];
43      	const Particle& JPsi = BS0.decayProducts()[ix].at( 443)[0];
44        FourMomentum ppipi = pip.mom()+pim.mom();
45        // mass cut and presence of f_0(980)
46        const double mpipi = ppipi.mass();
47        if(abs(mpipi-0.98)>0.9) continue;
48        if(count(BS0.decaying()[ix].children(), hasPID(9010221))!=1) continue;
49        // f_0 helicity angle
50        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(BS0.decaying()[ix].mom().betaVec());
51        FourMomentum ppsi  = boost1.transform(JPsi.mom());
52        Vector3 axis1 = ppsi.p3().unit();
53        ppipi = boost1.transform(ppipi);
54        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
55        FourMomentum ppip = boost2.transform(boost1.transform(pip.mom()));
56        _h[1]->fill(ppip.p3().unit().dot(axis1));
57        // helicity angle find J.psi leptonic children
58        if (JPsi.children().size()!=2) continue;
59        if (JPsi.children()[0].pid()!=-JPsi.children()[1].pid()) continue;
60        if (JPsi.children()[0].abspid()!=PID::EMINUS &&
61            JPsi.children()[0].abspid()!=PID::MUON) continue;
62        Particle lm = JPsi.children()[0];
63        Particle lp = JPsi.children()[1];
64        if (lm.pid()<0) swap(lm,lp);
65        LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(ppsi.betaVec());
66        FourMomentum plp = boost3.transform(boost1.transform(lp.mom()));
67        _h[0]->fill(-plp.p3().unit().dot(axis1));
68      }
69    }
70
71
72    /// Normalise histograms etc., after the run
73    void finalize() {
74      normalize(_h, 1.0, false);
75    }
76
77    /// @}
78
79
80    /// @name Histograms
81    /// @{
82    Histo1DPtr _h[2];
83    /// @}
84
85
86  };
87
88
89  RIVET_DECLARE_PLUGIN(LHCB_2013_I1081268);
90
91}