Rivet analyses

e⁺e⁻ → (DD̄^*)^±π^∓ for $\sqrt{s}=4.26$ GeV

Experiment: BESIII (BEPC)

Inspire ID: 1256939

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 112 (2014) 2, 022001

Beams: e+ e-

Beam energies: (2.1, 2.1)GeV

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

Measurement of mass distributions for e⁺e⁻ → (DD̄^*)^±π^∓ for $\sqrt{s}=4.26$ GeV by BES. The cross section for e⁺e⁻ → Z_c(3885)^±π^∓ → (DD̄^*)^±π^∓ is also measured. As there is no PDG code for the $Z_c(3885)^+ we take it to be 9044213, although this can be changed using the PID option.

Source code:`BESIII_2013_I1256939.cc`

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

namespace Rivet {


  /// @brief e+e-> Z+- pi-+
  class BESIII_2013_I1256939 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2013_I1256939);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // set the PDG code
      _pid = getOption<double>("PID", 9044213);
      // projections
      declare(Beam(), "Beams");
      declare(FinalState(), "FS");
      // histograms
      book(_sigma, 1, 1, 1);
      for (unsigned int ix = 0; ix < 2; ++ix) {
        book(_h[ix], 2, 1, 1 + ix);
      }
      book(_h[2], 3, 1, 1);
    }


    /// 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;
      if (beams.first.pid() > 0) {
        axis = beams.first.momentum().p3().unit();
      }
      else {
        axis = beams.second.momentum().p3().unit();
      }
      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.momentum(), parent.momentum())) {
              found = true;
              break;
            }
          }
          if (!found) DD.push_back(parent);
        }
        else {
          other.push_back(p);
        }
      }
      // D Dbar + charged pion
      if (DD.size() != 2 || other.size() != 1) vetoEvent;
      if (DD[0].pid() * DD[1].pid() > 0) vetoEvent;
      if (other[0].abspid() != 211) vetoEvent;
      if (DD[0].abspid() % 10 != 3) swap(DD[0], DD[1]);
      if (DD[0].abspid() % 10 != 3 || DD[1].abspid() % 10 != 1) vetoEvent;
      const double mass = (DD[0].momentum() + DD[1].momentum()).mass();
      const double cTheta = abs(axis.dot(other[0].momentum().p3().unit()));
      unsigned int iloc = 0;
      // D0 D*- pi+ +cc
      if ((DD[0].pid() == -413 && DD[1].pid() == 421 && other[0].pid() == 211)
          || (DD[0].pid() == 413 && DD[1].pid() == -421 && other[0].pid() == -211)) {
        iloc = 0;
      }
      // D- D*0 pi+ +cc
      else if ((DD[0].pid() == 423 && DD[1].pid() == -411 && other[0].pid() == 211)
               || (DD[0].pid() == -423 && DD[1].pid() == 411 && other[0].pid() == -211)) {
        iloc = 1;
      }
      // otherwise veto event
      else {
        vetoEvent;
      }
      _h[iloc]->fill(mass);
      // parent Z+/-
      if (DD[0].parents()[0].abspid() == _pid && DD[1].parents()[0].abspid() == _pid
          && fuzzyEquals(DD[0].parents()[0].momentum(), DD[1].parents()[0].momentum())) {
        _sigma->fill("4.26"s);
        _h[2]->fill(cTheta);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_sigma, crossSection() / sumOfWeights() / picobarn);
      for (unsigned int ix = 0; ix < 3; ++ix) {
        normalize(_h[ix], 1.0, false);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _sigma;
    Histo1DPtr _h[3];
    int _pid;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2013_I1256939);

}

Rivet analyses

e+e− → (DD̄*)±π∓ for $\sqrt{s}=4.26$ GeV

Source code:BESIII_2013_I1256939.cc

e⁺e⁻ → (DD̄^*)^±π^∓ for $\sqrt{s}=4.26$ GeV

Source code:`BESIII_2013_I1256939.cc`