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. 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// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief D_1 and D_2 decay distributions
  9  class BABAR_2010_I867611 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2010_I867611);
 14
 15
 16    /// @name Analysis methods
 17    /// @{
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21
 22      // Initialise and register projections
 23      declare(UnstableParticles(), "UFS");
 24
 25      // Book histograms
 26      book(_h_D1_ctheta, 1,1,1);
 27      book(_h_D2_ctheta, 1,1,2);
 28      book(_h_D02S_ctheta, 1,1,3);
 29      book(_h_DStar02S_ctheta, 1,1,4);
 30      book(_h_D3_ctheta, 1,1,5);
 31    }
 32
 33    /// Recursively walk the decay tree to find decay products of @a p
 34    void findDecayProducts(Particle mother, Particles& dstar, Particles& d0, Particles& pi, unsigned int& ncount) {
 35      for(const Particle & p: mother.children()) {
 36        if(p.abspid()==413)
 37          dstar.push_back(p);
 38        else if(p.abspid()==421)
 39          d0.push_back(p);
 40        else if(p.abspid()==211)
 41          pi.push_back(p);
 42        ncount +=1;
 43      }
 44    }
 45
 46    /// Perform the per-event analysis
 47    void analyze(const Event& event) {
 48      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==425 || Cuts::abspid==10423 ||
 49                                                                               Cuts::abspid==100421 || Cuts::abspid==100423 ||
 50                                                                               Cuts::abspid==427)) {
 51        // decay products
 52        Particles dstar,d0,pi;
 53        unsigned int ncount=0;
 54        findDecayProducts(p,dstar,d0, pi,ncount);
 55        if(ncount!=2 || dstar.size()!=1 || pi.size()!=1 || d0.size()!=0 ) continue;
 56        if(dstar[0].pid()/p.pid()<0) continue;
 57        Particle p2 = dstar[0];
 58        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p2.momentum().betaVec());
 59        Vector3 d1 = boost.transform(pi[0].momentum()).p3().unit();
 60        ncount=0;
 61        dstar.clear();
 62        d0.clear();
 63        pi.clear();
 64        findDecayProducts(p2,dstar,d0, pi,ncount);
 65        if(ncount!=2 || dstar.size()!=0 || pi.size()!=1 || d0.size()!=1 ) continue;
 66        if(pi[0].pid()/p2.pid()<0) continue;
 67        Vector3 d2 = boost.transform(pi[0].momentum()).p3().unit();
 68        double cTheta  = d1.dot(d2);
 69        // decay angles
 70        if(p.abspid()==425)
 71          _h_D2_ctheta->fill(cTheta);
 72        else if(p.abspid()==10423)
 73          _h_D1_ctheta->fill(cTheta);
 74        else if(p.abspid()==100421)
 75          _h_D02S_ctheta->fill(cTheta);
 76        else if(p.abspid()==100423)
 77          _h_DStar02S_ctheta->fill(cTheta);
 78        else if(p.abspid()==427)
 79          _h_D3_ctheta->fill(cTheta);
 80      }
 81    }
 82
 83    /// Normalise histograms etc., after the run
 84    void finalize() {
 85      normalize(_h_D1_ctheta);
 86      normalize(_h_D2_ctheta);
 87      normalize(_h_D02S_ctheta);
 88      normalize(_h_DStar02S_ctheta);
 89      normalize(_h_D3_ctheta);
 90    }
 91
 92    /// @}
 93
 94
 95    /// @name Histograms
 96    /// @{
 97    Histo1DPtr _h_D1_ctheta,_h_D2_ctheta,_h_D02S_ctheta;
 98    Histo1DPtr _h_DStar02S_ctheta,_h_D3_ctheta;
 99    /// @}
100
101  };
102
103
104
105  RIVET_DECLARE_PLUGIN(BABAR_2010_I867611);
106
107}