Rivet analyses

e⁺e⁻ → J/ψDD̄ at $\sqrt{s}=10.58$GeV

Experiment: BELLE (KEKB)

Inspire ID: 1590028

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

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⁻ → J/ψDD̄ at $\sqrt{s}=10.58$GeV by BELLE. The cross section for e⁺e⁻ → J/ψX^*(3860)( → DD̄) is also measured for production at the energies of the Υ(1 → 5S) states and in the continuum at 10.52GeV. The status of the X^*(3860) is not clear, although it is characterized as a χ_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`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/FinalState.hh"

namespace Rivet {


  /// @brief e+ e- > J/psi D Dbar
  class BELLE_2017_I1590028 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2017_I1590028);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // set the PDG code
      _pid = getOption<int>("PID", 9010441);
      // projections
      declare(Beam(), "Beams");
      declare(FinalState(), "FS");
      // histograms
      if (isCompatibleWithSqrtS(10.58, 1e-4)) {
        for (size_t ix = 0; ix < 6; ++ix) {
          book(_h[ix], 1, 1, 1 + ix);
        }
      }
      book(_sigma, 2, 1, 1);
      for (const string& en : _sigma.binning().edges<0>()) {
        const double eval = stod(en) * GeV;
        if (isCompatibleWithSqrtS(eval, 1e-4)) {
          _sqs = en;
          break;
        }
      }
      raiseBeamErrorIf(_sqs.empty());
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // get the axis, direction of incoming electron
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      FourMomentum pep;
      if (beams.first.pid() > 0) {
        axis = beams.first.mom().p3().unit();
        pep = beams.second.mom();
      }
      else {
        axis = beams.second.mom().p3().unit();
        pep = beams.first.mom();
      }
      Particles fs = apply<FinalState>(event, "FS").particles();
      Particles DD, JPSI, other;
      for (const Particle& p : fs) {
        Particle parent = p;
        while (!parent.parents().empty()) {
          parent = parent.parents()[0];
          if (parent.abspid() == PID::DPLUS || parent.abspid() == PID::D0 || parent.pid() == PID::JPSI) break;
        }
        if (parent.abspid() != PID::DPLUS && parent.abspid() != PID::D0 && parent.pid() != PID::JPSI) {
          other.push_back(p);
          continue;
        }
        bool found = false;
        for (const auto& D : parent.pid() == PID::JPSI ? JPSI : DD) {
          // D or J/psi already in list
          if (fuzzyEquals(D.mom(), parent.mom())) {
            found = true;
            break;
          }
        }
        if (!found) {
          (parent.pid() == PID::JPSI ? JPSI : DD).push_back(parent);
        }
      }
      // require J/psi D Dbar
      if (JPSI.size() != 1 || DD.size() != 2 || other.size() != 0) vetoEvent;
      if (DD[0].pid() != -DD[1].pid()) vetoEvent;
      FourMomentum pDD = DD[0].mom() + DD[1].mom();
      // cross section
      if (DD[0].parents()[0].pid() == _pid && DD[1].parents()[0].pid() == _pid) {
        _sigma->fill(_sqs);
      }
      // histograms only at 10.58GeV
      if (!isCompatibleWithSqrtS(10.58, 1e-4)) vetoEvent;
      _h[0]->fill(pDD.mass() / GeV);
      const double cProd = axis.dot(JPSI[0].mom().p3().unit());
      _h[1]->fill(cProd);
      // finally the leptons from J/psi decay
      if (JPSI[0].children().size() != 2) vetoEvent;
      if (JPSI[0].children()[0].pid() != -JPSI[0].children()[1].pid()) vetoEvent;
      if (JPSI[0].children()[0].abspid() != PID::EMINUS && JPSI[0].children()[0].abspid() != PID::MUON)
        vetoEvent;
      Particle lm = JPSI[0].children()[0];
      Particle lp = JPSI[0].children()[1];
      // variables in J/psi frame
      Vector3 axis2 = -pDD.p3().unit();
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(JPSI[0].mom().betaVec());
      FourMomentum plm = boost1.transform(lm.mom());
      Vector3 axis4 = plm.p3().unit();
      double cPsi = axis2.dot(axis4);
      _h[2]->fill(cPsi);
      Vector3 axis3 = boost1.transform(pep).p3().unit();
      Vector3 aep = axis3 - axis3.dot(axis2) * axis2;
      Vector3 alm = axis4 - axis4.dot(axis2) * axis2;
      double phil = atan2(-axis2.cross(aep).dot(alm), aep.dot(alm));
      _h[4]->fill(phil);
      // variables in DD frame
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDD.betaVec());
      FourMomentum pD = boost2.transform((DD[0].pid() > 0 ? DD[0] : DD[1]).mom());
      Vector3 axisD = pD.p3().unit();
      axis2 *= -1;
      double cX = axis2.dot(axisD);
      _h[3]->fill(cX);
      axis3 = boost2.transform(pep).p3().unit();
      aep = axis3 - axis3.dot(axis2) * axis2;
      alm = axisD - axisD.dot(axis2) * axis2;
      phil = atan2(-axis2.cross(aep).dot(alm), aep.dot(alm));
      _h[5]->fill(phil);
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h, 1.0, false);
      scale(_sigma, crossSection() / sumOfWeights() / femtobarn);
    }

    /// @}


    /// @name Histograms
    /// @{
    int _pid;
    Histo1DPtr _h[6];
    BinnedHistoPtr<string> _sigma;
    string _sqs = "";
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2017_I1590028);

}

Rivet analyses

e+e− → J/ψDD̄ at $\sqrt{s}=10.58$GeV

Source code:BELLE_2017_I1590028.cc

e⁺e⁻ → J/ψDD̄ at $\sqrt{s}=10.58$GeV

Source code:`BELLE_2017_I1590028.cc`