Rivet analyses

π+π− mass distribution in X(3872 and ψ(2S) to J/ψπ+π−

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 π+π− mass distribution in the decays X(3872 and ψ(2S) to J/ψπ+π− measureed by BaBaR in B → JψK−π+π− decays. The background subtracted data were read from figure 3 in the paper. There is no consensus as to the nature of the χc1(3872) cc̄ state and therefore we taken its PDG code to be 9030443, i.e. the first unused code for an undetermined spin one cc̄ 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++ -*-
#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);

}