Rivet analyses

e+e− → (DD*)0π0 for $\sqrt{s}=4.226$ and 4.257 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1393996

Status: VALIDATED NOHEPDATA SINGLEWEIGHT

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 115 (2015) 22, 222002

Beams: e+ e-

Beam energies: (2.1, 2.1); (2.1, 2.1)GeV

Run details: - e+ e- to hadrons, pi0 set stable

Measurement of mass distributions for e+e− → (DD*)0π0 for $\sqrt{s}=4.226$ and 4.257 GeV by BES. The cross section for e+e− → Zc(3885)0π0 → (DD*)0π0 is also measured. As there is no PDG code for the Zc(3885)0 we take it to be the first unused exotic cc̄ value 9030443, although this can be changed using the PID option.

Source code:BESIII_2015_I1393996.cc

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

namespace Rivet {


  /// @brief e+ e- > Z0 pi0
  class BESIII_2015_I1393996 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1393996);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // set the PDG code
      _pid = getOption<double>("PID", 9030443);
      // projections
      declare(FinalState(), "FS");
      // histograms
      if (isCompatibleWithSqrtS(4.226))
        _sqs = "4.226";
      else if (isCompatibleWithSqrtS(4.257))
        _sqs = "4.257";
      raiseBeamErrorIf(_sqs.empty());
      for (size_t ix = 0; ix < 2; ++ix) {
        book(_h["4.257"s + toString(ix)], 2, ix + 1, 1);
        book(_h["4.226"s + toString(ix)], 2, ix + 1, 2);
      }
      book(_h["2"], 3, 1, 1);
      book(_sigma, 1, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Particles fs = apply<FinalState>(event, "FS").particles();
      Particles DD, other;
      for (const Particle& p : fs) {
        Particle parent = p;
        while (!parent.parents().empty()) {
          parent = parent.parents()[0];
          if (parent.abspid() == 411 || parent.abspid() == 413 || parent.abspid() == 421
              || parent.abspid() == 423)
            break;
        }
        if ((parent.abspid() == 411 || parent.abspid() == 421) && !parent.parents().empty()) {
          Particle Dstar = parent.parents()[0];
          if (Dstar.abspid() == 413 || Dstar.abspid() == 423) parent = Dstar;
        }
        if (parent.abspid() == 411 || parent.abspid() == 413 || parent.abspid() == 421
            || parent.abspid() == 423) {
          bool found = false;
          for (const auto& D : DD) {
            // D already in list
            if (fuzzyEquals(D.mom(), parent.mom())) {
              found = true;
              break;
            }
          }
          if (!found) DD.push_back(parent);
        }
        else {
          other.push_back(p);
        }
      }
      // D Dbar + neutral pion
      if (DD.size() != 2 || other.size() != 1) vetoEvent;
      if (DD[0].pid() * DD[1].pid() > 0) vetoEvent;
      if (other[0].pid() != 111) vetoEvent;
      // D pi mass greater than 2.1
      for (unsigned int ix = 0; ix < 2; ++ix) {
        if (DD[ix].abspid() % 10 == 1 && (DD[ix].momentum() + other[0].momentum()).mass() < 2.1) vetoEvent;
      }
      double mass = (DD[0].momentum() + DD[1].momentum()).mass();
      unsigned int iloc = 0;
      // D+ D*+
      if ((DD[0].abspid() == 413 && DD[1].abspid() == 411)
          || (DD[1].abspid() == 413 && DD[0].abspid() == 411)) {
        iloc = 0;
      }
      // D0 D*0
      else if ((DD[0].abspid() == 423 && DD[1].abspid() == 421)
               || (DD[1].abspid() == 423 && DD[0].abspid() == 421)) {
        iloc = 1;
      }
      // otherwise veto event
      else
        vetoEvent;
      _h[_sqs + toString(iloc)]->fill(mass);
      _h["2"]->fill(mass);
      // parent Z0
      if (DD[0].parents()[0].pid() == _pid && DD[1].parents()[0].pid() == _pid
          && fuzzyEquals(DD[0].parents()[0].mom(), DD[1].parents()[0].mom()))
        _sigma->fill(_sqs);
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _sigma;
    map<string, Histo1DPtr> _h;
    string _sqs = "";
    int _pid;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2015_I1393996);

}