Rivet analyses

title: BESIII_2013_I1247675

$e^+e^-\to (D^\bar{D}^)^\pm\pi^\mp$ for $\sqrt{s}=4.26$ GeV

Experiment: BESIII (BEPC)

Inspire ID: 1247675

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 112 (2014) 13, 132001

Beams: e+ e-

Beam energies: (2.1, 2.1)GeV

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

Measurement of mass distributions for $e^+e^-\to (D^\bar{D}^)^\pm\pi^\mp$ for $\sqrt{s}=4.26$ GeV by BES. The cross section for $e^+e^-\to Z_c(4025)^\pm\pi^\mp\to (D^\bar{D}^)^\pm\pi^\mp$ is also measured. As there is no PDG code for the $Z_c(4025)^+ we take it to be 9044213, although this can be changed using the PID option.

Source code:BESIII_2013_I1247675.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e-> Z(4025)+- pi-+ class BESIII_2013_I1247675 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2013_I1247675);


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

/// Book histograms and initialise projections before the run
void init() {
  // set the PDG code
  _pid = getOption<double>("PID", 9044213);
  // projections
  declare(FinalState(), "FS");
  // histograms
  book(_sigma, 1, 1, 1);
  book(_h, 2, 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() == 413 || parent.abspid() == 423) break;
    }
    if (parent.abspid() == 413 || 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].pid() == -413 && DD[1].pid() == 423 && other[0].pid() == 211)
      || (DD[0].pid() == 413 && DD[1].pid() == -423 && other[0].pid() == -211)
      || (DD[0].pid() == 423 && DD[1].pid() == -413 && other[0].pid() == 211)
      || (DD[0].pid() == -423 && DD[1].pid() == 413 && other[0].pid() == -211)) {
    const double mass = (DD[0].momentum() + DD[1].momentum()).mass();
    _h->fill(mass);
    // parent Z+/-
    if (DD[0].parents()[0].abspid() == _pid && DD[1].parents()[0].abspid() == _pid
        && fuzzyEquals(DD[0].parents()[0].mom(), DD[1].parents()[0].mom())) {
      _sigma->fill("4.26"s);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_sigma, crossSection() / sumOfWeights() / picobarn);
  normalize(_h, 1., false);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2013_I1247675);

} ```