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## Rivet analyses reference

### BABAR_2010_I867611

Helicity angle distributions in excited $D$ meson decays
Experiment: BABAR (PEP-II)
Inspire ID: 867611
Status: VALIDATED
Authors:
• Peter Richardson
References:
• Phys.Rev. D82 (2010) 111101
Beams: * *
Beam energies: ANY
Run details:
• Any process producing excited $D$ mesons

The decays $D^{**} \to D^{*+}\pi^-\to D^0\pi^+\pi^-$ are used to measure the helicity angle, i.e. the angle between the two pions in the rest frame of the $D^*$. The decays of $D_1(2420)^0$, $D^*_2(2460)^0$, $D(2550)^0$, $D^*(2600)$, $D(2750)$ were measured, but currently only the $D_1(2420)^0$, $D^*_2(2460)^0$ are implemented. The data were read from the plots in the papers and therefore for the $D_1(2420)^0$, $D^*_2(2460)^0$ the error bars are the size of the points in the plots.

Source code: BABAR_2010_I867611.cc
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 // -*- C++ -*- #include "Rivet/Analysis.hh" #include "Rivet/Projections/UnstableParticles.hh" namespace Rivet { /// @brief D_1 and D_2 decay distributions class BABAR_2010_I867611 : public Analysis { public: /// Constructor DEFAULT_RIVET_ANALYSIS_CTOR(BABAR_2010_I867611); /// @name Analysis methods //@{ /// Book histograms and initialise projections before the run void init() { // Initialise and register projections declare(UnstableParticles(), "UFS"); // Book histograms book(_h_D1_ctheta, 1,1,1); book(_h_D2_ctheta, 1,1,2); } /// Recursively walk the decay tree to find decay products of @a p void findDecayProducts(Particle mother, Particles & dstar, Particles & d0, Particles & pi,unsigned int & ncount) { for(const Particle & p: mother.children()) { if(p.abspid()==413) dstar.push_back(p); else if(p.abspid()==421) d0.push_back(p); else if(p.abspid()==211) pi.push_back(p); ncount +=1; } } /// Perform the per-event analysis void analyze(const Event& event) { for(const Particle& p : apply(event, "UFS").particles(Cuts::abspid==425 || Cuts::abspid==10423)) { // decay products Particles dstar,d0,pi; unsigned int ncount=0; findDecayProducts(p,dstar,d0, pi,ncount); if(ncount!=2 || dstar.size()!=1 || pi.size()!=1 || d0.size()!=0 ) continue; if(dstar[0].pid()/p.pid()<0) continue; Particle p2 = dstar[0]; LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p2.momentum().betaVec()); Vector3 d1 = boost.transform(pi[0].momentum()).p3().unit(); ncount=0; dstar.clear(); d0.clear(); pi.clear(); findDecayProducts(p2,dstar,d0, pi,ncount); if(ncount!=2 || dstar.size()!=0 || pi.size()!=1 || d0.size()!=1 ) continue; if(pi[0].pid()/p2.pid()<0) continue; Vector3 d2 = boost.transform(pi[0].momentum()).p3().unit(); double cTheta = d1.dot(d2); // decay angles if(p.abspid()==425) _h_D2_ctheta->fill(cTheta); else _h_D1_ctheta->fill(cTheta); } } /// Normalise histograms etc., after the run void finalize() { normalize(_h_D1_ctheta); normalize(_h_D2_ctheta); } //@} /// @name Histograms //@{ Histo1DPtr _h_D1_ctheta,_h_D2_ctheta; //@} }; // The hook for the plugin system DECLARE_RIVET_PLUGIN(BABAR_2010_I867611); }