Rivet analyses

title: BABAR_2005_I686354

$\pi^+\pi^-$ mass distribution in $Y(4260)\to J/\psi\pi^+\pi^-$

Experiment: BABAR (PEP-II)

Inspire ID: 686354

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 95 (2005) 142001

Beams: * *

Beam energies: ANY

Run details: - Any process producing psi(4230) for decays

Mass distribution in $Y(4260)\to J/\psi\pi^+\pi^-$ decays ($Y(4260)$ is now $\psi(4230)$). The background subtracted data were read from figure 3 in the paper. There is no consensus as to the nature of the $\psi(4230)$ $c\bar{c}$ state and therefore we taken its PDG code to be 9030443, i.e. the first unused code for an undetermined spin one $c\bar{c}$ state. This can be changed using the PID option if a different code is used by the event generator performing the simulation.

Source code:BABAR_2005_I686354.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Y(4260) -> pi+ pi_ J/psi class BABAR_2005_I686354 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2005_I686354);


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

/// Book histograms and initialise projections before the run
void init() {
  _pid = getOption<int>("PID", 9030443);
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == _pid);
  declare(ufs, "UFS");
  DecayedParticles PSI(ufs);
  PSI.addStable(443);
  declare(PSI, "PSI");
  // histograms
  book(_h, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 1}, {443, 1}};
  DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
  for (unsigned int ix = 0; ix < PSI.decaying().size(); ++ix) {
    if (!PSI.modeMatches(ix, 3, mode)) continue;
    const Particle& pip = PSI.decayProducts()[ix].at(211)[0];
    const Particle& pim = PSI.decayProducts()[ix].at(-211)[0];
    double mpipi = (pip.momentum() + pim.momentum()).mass();
    _h->fill(mpipi);
  }
}

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

/// @}


/// @name Histograms
/// @{
int _pid;
Histo1DPtr _h;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2005_I686354);

} ```