Rivet analyses

title: BABAR_2005_I651834

$\pi^+\pi^-$ mass distribution in $X(3872$ and $\psi(2S)$ to $J/\psi\pi^+\pi^-$

Experiment: BABAR (PEP-II)

Inspire ID: 651834

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 71 (2005) 071103

Beams: * *

Beam energies: ANY

Run details: - Any process producing psi(2S), X(3872), original B decays

The $\pi^+\pi^-$ mass distribution in the decays $X(3872$ and $\psi(2S)$ to $J/\psi\pi^+\pi^-$ measureed by BaBaR in $B\to J\psi K^-\pi^+\pi^-$ decays. The background subtracted data were read from figure 3 in the paper. There is no consensus as to the nature of the $\chi_{c1}(3872)$ $c\bar{c}$ 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_I651834.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief psi(2S)/X(3782) -> J/psi pi+pi- class BABAR_2005_I651834 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2005_I651834);


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

/// Book histograms and initialise projections before the run
void init() {
  // set the PDG code
  _pid = getOption<int>("PID", 9030443);
  // projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 100443 || Cuts::abspid == _pid);
  declare(ufs, "UFS");
  DecayedParticles PSI(ufs);
  PSI.addStable(443);
  declare(PSI, "PSI");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1 + ix, 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[PSI.decaying()[ix].pid() == _pid ? 0 : 1]->fill(mpipi);
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BABAR_2005_I651834);

} ```