Rivet analyses

title: BESIII_2012_I1128258

Mass distributions in $\chi_{cJ}\to p\bar{n}\pi^-$ and $p\bar{n}\pi^-\pi^0$

Experiment: BESIII (BEPC)

Inspire ID: 1128258

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 86 (2012) 052011

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_c0,1,2

Measurement of the mass distributions in the decays $\chi_{cJ}\to p\bar{n}\pi^-$ and $p\bar{n}\pi^-\pi^0$. The data were read from the plots in the paper and may not be corrected for backgrounds and efficiency.

Source code:BESIII_2012_I1128258.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief chi_c -> p nbar pi- p nbar pi- pi0 class BESIII_2012_I1128258 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1128258);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 10441 || Cuts::pid == 445 || Cuts::pid == 20444);
  declare(ufs, "UFS");
  DecayedParticles chi(ufs);
  chi.addStable(PID::PI0);
  declare(chi, "chi");
  // histograms
  for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 1, 1, 1 + ix);
  book(_h[3], 2, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode1 = {{2212, 1}, {-2112, 1}, {-211, 1}};
  static const map<PdgId, unsigned int>& mode1CC = {{-2212, 1}, {2112, 1}, {211, 1}};
  static const map<PdgId, unsigned int>& mode2 = {{2212, 1}, {-2112, 1}, {-211, 1}, {111, 1}};
  static const map<PdgId, unsigned int>& mode2CC = {{-2212, 1}, {2112, 1}, {211, 1}, {111, 1}};
  DecayedParticles chi = apply<DecayedParticles>(event, "chi");
  // loop over particles
  for (unsigned int ix = 0; ix < chi.decaying().size(); ++ix) {
    int mode = -1, sign = 0;
    if (chi.decaying()[ix].pid() == 10441) {
      if (chi.modeMatches(ix, 3, mode1)) {
        mode = 0;
        sign = 1;
      }
      else if (chi.modeMatches(ix, 3, mode1CC)) {
        mode = 0;
        sign = -1;
      }
    }
    if (mode == 0) {
      const Particle& pim = chi.decayProducts()[ix].at(-211 * sign)[0];
      const Particle& pp = chi.decayProducts()[ix].at(2212 * sign)[0];
      const Particle& nbar = chi.decayProducts()[ix].at(-2112 * sign)[0];
      _h[0]->fill((pp.momentum() + pim.momentum()).mass());
      _h[1]->fill((nbar.momentum() + pim.momentum()).mass());
      _h[2]->fill((pp.momentum() + nbar.momentum()).mass());
      continue;
    }
    else if (chi.modeMatches(ix, 4, mode2)) {
      mode = 1;
      sign = 1;
    }
    else if (chi.modeMatches(ix, 4, mode2CC)) {
      mode = 1;
      sign = -1;
    }
    else
      continue;
    const Particle& pim = chi.decayProducts()[ix].at(-211 * sign)[0];
    const Particle& pi0 = chi.decayProducts()[ix].at(111)[0];
    _h[3]->fill((pim.momentum() + pi0.momentum()).mass());
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 4; ++ix) normalize(_h[ix]);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[4];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2012_I1128258);

} ```