Rivet analyses referenceBESII_2005_I678943$\pi^+\pi^-$ mass distribution in $J/\psi\to 2\pi^+2\pi^-$Experiment: BESII (BEPC) Inspire ID: 678943 Status: VALIDATED NOHEPDATA Authors:
Beam energies: ANY Run details:
$\pi^+\pi^-$ mass distribution in $J/\psi\to 2\pi^+2\pi^-$. The uncorrected data was read from the figures in the paper, given the lack of corrections and background subtraction only the low background $J/\psi\to 2\pi^+2\pi^-$ mode is implemented and not the $\psi(2S)\to3\pi^+\pi^-$ distributions which have a large background. Source code: BESII_2005_I678943.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 $\pi^+\pi^-$ mass distribution in $J/\psi\to 2\pi^+2\pi^-$
10 class BESII_2005_I678943 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESII_2005_I678943);
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==443);
24 declare(ufs, "UFS");
25 DecayedParticles PSI(ufs);
26 declare(PSI, "PSI");
27 // histos
28 book(_h, 1, 1, 1);
29 }
30
31
32 /// Perform the per-event analysis
33 void analyze(const Event& event) {
34 // find the J/psi decays
35 DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
36 for (unsigned int ix=0; ix<PSI.decaying().size(); ++ix) {
37 if (!PSI.modeMatches(ix,4,mode)) continue;
38 const Particles& pip = PSI.decayProducts()[0].at( 211);
39 const Particles& pim = PSI.decayProducts()[0].at(-211);
40 bool kVeto=false;
41 vector<double> mpipi; mpipi.reserve(4);
42 for (unsigned int iy=0; iy<2; ++iy) {
43 for (unsigned int iy=0; iy<2; ++iy) {
44 double mpp = (pip[ix].mom()+pim[0].mom()).mass();
45 kVeto |= (mpp>0.47&&mpp<0.53);
46 mpipi.push_back(mpp);
47 }
48 }
49 if (kVeto) continue;
50 for (const double& m : mpipi) _h->fill(m);
51 }
52 }
53
54
55 /// Normalise histograms etc., after the run
56 void finalize() {
57 normalize(_h, 1.0, false);
58 }
59
60 /// @}
61
62
63 /// @name Histograms
64 /// @{
65 Histo1DPtr _h;
66 const map<PdgId,unsigned int> mode = { { 211,2}, { -211,2}};
67 /// @}
68
69
70 };
71
72
73 RIVET_DECLARE_PLUGIN(BESII_2005_I678943);
74
75}
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