Rivet analyses

title: BABAR_2021_I1867843

Dalitz plot analysis of $\eta_c\to K^+K^-\eta^\prime$, $\pi^+\pi^-\eta$ and $\pi^+\pi^-\eta^\prime$

Experiment: BABAR (PEP-II)

Inspire ID: 1867843

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 104 (2021) 7, 072002

Beams: * *

Beam energies: ANY

Run details: - Any process producing eta_c (originally gamma gamma -> chi_c)

Measurement of the mass distributions in the decays $\eta_c\to K^+K^-\eta^\prime$, $\pi^+\pi^-\eta$ and $\pi^+\pi^-\eta^\prime$ by BaBar. The data were read from the plots in the paper and therefore for some points the error bars are the size of the point. Also the sideband background from the plots has been subtracted. It is also not clear that any resolution effects have been unfolded.

Source code:BABAR_2021_I1867843.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief eta_c Dalitz decays class BABAR_2021_I1867843 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2021_I1867843);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 441);
  declare(ufs, "UFS");
  DecayedParticles ETAC(ufs);
  ETAC.addStable(PID::PI0);
  ETAC.addStable(PID::K0S);
  ETAC.addStable(PID::ETA);
  ETAC.addStable(PID::ETAPRIME);
  declare(ETAC, "ETAC");
  // histograms
  book(_h_KK, 1, 1, 1);
  book(_h_etaPK, 1, 1, 2);
  book(_h_pipi1, 2, 1, 1);
  book(_h_etaPpi, 2, 1, 2);
  book(_h_pipi2, 3, 1, 1);
  book(_h_etapi, 3, 1, 2);
  book(_dalitz1, "dalitz1", 50, 2., 6.5, 50, 2., 6.5);
  book(_dalitz2, "dalitz2", 50, 0., 9., 50, 0., 9.);
  book(_dalitz3, "dalitz3", 50, 0., 8., 50, 0., 8.);
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode1 = {{321, 1}, {-321, 1}, {331, 1}};
  static const map<PdgId, unsigned int>& mode2 = {{211, 1}, {-211, 1}, {331, 1}};
  static const map<PdgId, unsigned int>& mode3 = {{211, 1}, {-211, 1}, {221, 1}};
  DecayedParticles ETAC = apply<DecayedParticles>(event, "ETAC");
  // loop over particles
  for (unsigned int ix = 0; ix < ETAC.decaying().size(); ++ix) {
    //K+ K- eta'
    if (ETAC.modeMatches(ix, 3, mode1) && ETAC.decaying()[ix].mass() > 2.93
        && ETAC.decaying()[ix].mass() < 3.03) {
      const Particle& Kp = ETAC.decayProducts()[ix].at(321)[0];
      const Particle& Km = ETAC.decayProducts()[ix].at(-321)[0];
      const Particle& etaP = ETAC.decayProducts()[ix].at(331)[0];
      double mplus = (Kp.momentum() + etaP.momentum()).mass2();
      double mminus = (Km.momentum() + etaP.momentum()).mass2();
      double mKK = (Kp.momentum() + Km.momentum()).mass2();
      _h_KK->fill(sqrt(mKK));
      _h_etaPK->fill(sqrt(mplus));
      _h_etaPK->fill(sqrt(mminus));
      _dalitz1->fill(mplus, mminus);
    }
    // pi+ pi- eta'
    else if (ETAC.modeMatches(ix, 3, mode2) && ETAC.decaying()[ix].mass() > 2.93
             && ETAC.decaying()[ix].mass() < 3.03) {
      const Particle& pip = ETAC.decayProducts()[ix].at(211)[0];
      const Particle& pim = ETAC.decayProducts()[ix].at(-211)[0];
      const Particle& etaP = ETAC.decayProducts()[ix].at(331)[0];
      double mplus = (pip.momentum() + etaP.momentum()).mass2();
      double mminus = (pim.momentum() + etaP.momentum()).mass2();
      double mpipi = (pip.momentum() + pim.momentum()).mass2();
      _h_pipi1->fill(sqrt(mpipi));
      _h_etaPpi->fill(sqrt(mplus));
      _h_etaPpi->fill(sqrt(mminus));
      _dalitz2->fill(mplus, mminus);
    }
    // pi+ pi- eta
    else if (ETAC.modeMatches(ix, 3, mode3) && ETAC.decaying()[ix].mass() > 2.92
             && ETAC.decaying()[ix].mass() < 3.02) {
      const Particle& pip = ETAC.decayProducts()[ix].at(211)[0];
      const Particle& pim = ETAC.decayProducts()[ix].at(-211)[0];
      const Particle& eta = ETAC.decayProducts()[ix].at(221)[0];
      double mplus = (pip.momentum() + eta.momentum()).mass2();
      double mminus = (pim.momentum() + eta.momentum()).mass2();
      double mpipi = (pip.momentum() + pim.momentum()).mass2();
      _h_pipi2->fill(sqrt(mpipi));
      _h_etapi->fill(sqrt(mplus));
      _h_etapi->fill(sqrt(mminus));
      _dalitz3->fill(mplus, mminus);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_KK);
  normalize(_h_etaPK);
  normalize(_h_pipi1);
  normalize(_h_etaPpi);
  normalize(_h_pipi2);
  normalize(_h_etapi);
  normalize(_dalitz1);
  normalize(_dalitz2);
  normalize(_dalitz3);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_KK, _h_etaPK;
Histo1DPtr _h_pipi1, _h_etaPpi;
Histo1DPtr _h_pipi2, _h_etapi;
Histo2DPtr _dalitz1, _dalitz2, _dalitz3;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2021_I1867843);

} ```