Rivet analyses

title: LHCB_2018_I1704426

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

Experiment: LHCB (LHC)

Inspire ID: 1704426

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - JHEP 02 (2019) 126

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons

Measurement of the mass distributions in the decay $D^0\to K^+K^-\pi^+\pi^-$ by LHCb. The data were extracted from the plots in the paper. It is also not clear that any resolution effects have been unfolded.

Source code:LHCB_2018_I1704426.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief class LHCB_2018_I1704426 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2018_I1704426);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 421);
  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");
  // histograms
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // define the decay mode
  static const map<PdgId, unsigned int>& mode = {{321, 1}, {-321, 1}, {211, 1}, {-211, 1}};
  DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
  // loop over particles
  for (unsigned int ix = 0; ix < D0.decaying().size(); ++ix) {
    int sign = D0.decaying()[ix].pid() / 421;
    if (D0.modeMatches(ix, 4, mode)) {
      const Particles& Kp = D0.decayProducts()[ix].at(sign * 321);
      const Particles& Km = D0.decayProducts()[ix].at(-sign * 321);
      const Particles& pip = D0.decayProducts()[ix].at(sign * 211);
      const Particles& pim = D0.decayProducts()[ix].at(-sign * 211);
      double mpipi = (pip[0].momentum() + pim[0].momentum()).mass();
      if (mpipi > 0.4802 && mpipi < 0.5072) continue;
      _h[0]->fill((Kp[0].momentum() + Km[0].momentum()).mass() / MeV);
      _h[1]->fill(mpipi / MeV);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h[ix], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
/// @}

};

RIVET_DECLARE_PLUGIN(LHCB_2018_I1704426);

} ```