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BELLE_2017_I1590028

$e^+e^-\to J/\psi D\bar{D}$ at $\sqrt{s}=10.58$GeV
Experiment: BELLE (KEKB)
Inspire ID: 1590028
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson <peter.richardson@durham.ac.uk?
References:
  • Phys.Rev.D 95 (2017) 112003
Beams: e+ e-
Beam energies: (4.7, 4.7); (5.0, 5.0); (5.2, 5.2); (5.3, 5.3); (5.3, 5.3); (5.4, 5.4) GeV
Run details:
  • e+ e- > hadrons

Measurement of mass and angular distributions in $e^+e^-\to J/\psi D\bar{D}$ at $\sqrt{s}=10.58$GeV by BELLE. The cross section for $e^+e^-\to J/\psi X^*(3860)(\to D\bar{D}$) is also measured for production at the energies of the $\Upsilon(1\to5S)$ states and in the continuum at 10.52GeV. The status of the $X^*(3860)$ is not clear, although it is characterized as a $\chi_{c0}$ state we therefore take the PDG code to be 9010441, which can be changed using the PID option

Source code: BELLE_2017_I1590028.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/Beam.hh"
  4#include "Rivet/Projections/FinalState.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief e+ e- > J/psi D Dbar
 10  class BELLE_2017_I1590028 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2017_I1590028);
 15
 16
 17    /// @name Analysis methods
 18    /// @{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      // set the PDG code
 23      _pid = getOption<int>("PID", 9010441);
 24      // projections
 25      declare(Beam(), "Beams");
 26      declare(FinalState(), "FS");
 27      // histograms
 28      if(isCompatibleWithSqrtS(10.58,1e-4)) {
 29	// histograms
 30	for(unsigned int ix=0;ix<6;++ix) {
 31	  book(_h[ix],1,1,1+ix);
 32	}
 33      }
 34      book(_sigma,2,1,1);
 35      for (const string& en : _sigma.binning().edges<0>()) {
 36        const double end = std::stod(en)*GeV;
 37        if (isCompatibleWithSqrtS(end,1e-4)) {
 38          _ecms = en;
 39          break;
 40        }
 41      }
 42      if (_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
 43    }
 44
 45
 46    /// Perform the per-event analysis
 47    void analyze(const Event& event) {
 48      // get the axis, direction of incoming electron
 49      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 50      Vector3 axis;
 51      FourMomentum pep;
 52      if (beams.first.pid()>0) {
 53        axis = beams.first .mom().p3().unit();
 54        pep  = beams.second.mom();
 55      }
 56      else {
 57        axis = beams.second.mom().p3().unit();
 58        pep  = beams.first .mom();
 59      }
 60      Particles fs = apply<FinalState>(event, "FS").particles();
 61      Particles DD,JPSI,other;
 62      for (const Particle& p : fs) {
 63        Particle parent=p;
 64        while (!parent.parents().empty()) {
 65          parent=parent.parents()[0];
 66          if (parent.abspid()==PID::DPLUS ||
 67              parent.abspid()==PID::D0||
 68              parent.pid()   ==PID::JPSI) break;
 69        }
 70        if (parent.abspid()!=PID::DPLUS &&
 71            parent.abspid()!=PID::D0    &&
 72            parent.pid()   !=PID::JPSI) {
 73          other.push_back(p);
 74          continue;
 75        }
 76        bool found=false;
 77        for (const auto& D : parent.pid()==PID::JPSI ? JPSI : DD) {
 78          // D or J/psi already in list
 79          if (fuzzyEquals(D.mom(),parent.mom())) {
 80            found=true;
 81            break;
 82          }
 83        }
 84        if (!found) {
 85          (parent.pid()==PID::JPSI ? JPSI : DD).push_back(parent);
 86        }
 87      }
 88      // require J/psi D Dbar
 89      if (JPSI.size()!=1 || DD.size()!=2 || other.size()!=0) vetoEvent;
 90      if (DD[0].pid()!=-DD[1].pid()) vetoEvent;
 91      FourMomentum pDD = DD[0].mom()+DD[1].mom();
 92      // cross section
 93      if(DD[0].parents()[0].pid()==_pid && DD[1].parents()[0].pid()==_pid) {
 94	_sigma->fill(_ecms);
 95      }
 96      // histograms only at 10.58GeV
 97      if(!_h[0]) return;
 98      _h[0]->fill(pDD.mass());
 99      const double cProd = axis.dot(JPSI[0].mom().p3().unit());
100      _h[1]->fill(cProd);
101      // finally the leptons from J/psi decay
102      if (JPSI[0].children().size()!=2) vetoEvent;
103      if (JPSI[0].children()[0].pid()!=-JPSI[0].children()[1].pid()) vetoEvent;
104      if (JPSI[0].children()[0].abspid()!=PID::EMINUS &&
105      JPSI[0].children()[0].abspid()!=PID::MUON) vetoEvent;
106      Particle lm = JPSI[0].children()[0];
107      Particle lp = JPSI[0].children()[1];
108      // variables in J/psi frame
109      Vector3 axis2 = -pDD.p3().unit();
110      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(JPSI[0].mom().betaVec());
111      FourMomentum plm = boost1.transform(lm.mom());
112      Vector3 axis4 = plm.p3().unit();
113      double cPsi = axis2.dot(axis4);
114      _h[2]->fill(cPsi);
115      Vector3 axis3 = boost1.transform(pep).p3().unit();
116      Vector3 aep = axis3-axis3.dot(axis2)*axis2;
117      Vector3 alm = axis4-axis4.dot(axis2)*axis2;
118      double phil = atan2(-axis2.cross(aep).dot(alm),aep.dot(alm));
119      _h[4]->fill(phil);
120      // variables in DD frame
121      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDD.betaVec());
122      FourMomentum pD = boost2.transform((DD[0].pid()>0 ? DD[0] : DD[1]).mom());
123      Vector3 axisD = pD.p3().unit();
124      axis2 *= -1;
125      double cX = axis2.dot(axisD);
126      _h[3]->fill(cX);
127      axis3 = boost2.transform(pep).p3().unit();
128      aep = axis3-axis3.dot(axis2)*axis2;
129      alm = axisD-axisD.dot(axis2)*axis2;
130      phil = atan2(-axis2.cross(aep).dot(alm),aep.dot(alm));
131      _h[5]->fill(phil);
132    }
133
134
135    /// Normalise histograms etc., after the run
136    void finalize() {
137      normalize(_h, 1.0, false);
138      scale(_sigma,crossSection()/ sumOfWeights() /femtobarn);
139    }
140
141    /// @}
142
143
144    /// @name Histograms
145    /// @{
146    int _pid;
147    Histo1DPtr _h[6];
148    BinnedHistoPtr<string> _sigma;
149    string _ecms;
150    /// @}
151
152  };
153
154
155  RIVET_DECLARE_PLUGIN(BELLE_2017_I1590028);
156
157}