Rivet analyses

title: BESIII_2019_I1714778

Mass distributions in the decay $D^+\to K^0_S\pi^+\pi^+\pi^-$

Experiment: BESIII (BEPC)

Inspire ID: 1714778

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 100 (2019) 7, 072008

Beams: * *

Beam energies: ANY

Run details: none listed

Measurement of the mass distributions in the decay $D^+\to K^0_S\pi^+\pi^+\pi^-$ by BES. The data were read from the plots in the paper and therefore for some points the error bars are the size of the point. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2019_I1714778.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D+ -> KS0 pi+pi+pi- class BESIII_2019_I1714778 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1714778);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 411);
  declare(ufs, "UFS");
  DecayedParticles D0(ufs);
  D0.addStable(PID::PI0);
  D0.addStable(PID::K0S);
  D0.addStable(PID::ETA);
  D0.addStable(PID::ETAPRIME);
  declare(D0, "D0");
  // histos
  for (unsigned int ix = 0; ix < 9; ++ix) book(_h[ix], 1, 1, 1 + ix);
}

void findDecayProducts(const Particle& mother,
                       unsigned int& nstable,
                       Particles& pip,
                       Particles& pim,
                       Particles& K0) {
  for (const Particle& p : mother.children()) {
    int id = p.pid();
    if (id == PID::PIPLUS) {
      pip.push_back(p);
      ++nstable;
    }
    else if (id == PID::PIMINUS) {
      pim.push_back(p);
      ++nstable;
    }
    else if (id == PID::K0S) {
      K0.push_back(p);
      ++nstable;
    }
    else if (id == PID::KPLUS || id == PID::KMINUS || id == PID::PI0 || id == PID::K0L) {
      ++nstable;
    }
    else if (!p.children().empty()) {
      findDecayProducts(p, nstable, pip, pim, K0);
    }
    else
      ++nstable;
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  for (const Particle& meson : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == 411)) {
    unsigned int nstable(0);
    Particles pip, pim, K0;
    findDecayProducts(meson, nstable, pip, pim, K0);
    if (nstable != 4) continue;
    if (meson.pid() < 0) {
      swap(pim, pip);
    }
    if (pip.size() == 2 && pim.size() == 1 && K0.size() == 1) {
      double mpippim[2] = {(pim[0].momentum() + pip[0].momentum()).mass(),
                           (pim[0].momentum() + pip[1].momentum()).mass()};
      if (mpippim[0] > mpippim[1]) {
        swap(pip[0], pip[1]);
        swap(mpippim[0], mpippim[1]);
      }
      _h[0]->fill((K0[0].momentum() + pim[0].momentum()).mass());
      _h[1]->fill((K0[0].momentum() + pip[0].momentum()).mass());
      _h[2]->fill((K0[0].momentum() + pip[1].momentum()).mass());
      _h[3]->fill(mpippim[0]);
      _h[4]->fill(mpippim[1]);
      _h[5]->fill((K0[0].momentum() + pim[0].momentum() + pip[0].momentum()).mass());
      _h[6]->fill((K0[0].momentum() + pim[0].momentum() + pip[1].momentum()).mass());
      _h[7]->fill((pim[0].momentum() + pip[0].momentum() + pip[1].momentum()).mass());
      _h[8]->fill((pip[0].momentum() + pip[1].momentum()).mass());
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 9; ++ix) normalize(_h[ix], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[9];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2019_I1714778);

} ```