Rivet analyses

π⁺π⁻ spectrum in ψ(2S) → π⁺π⁻J/ψ

Experiment: MARKII (SPEAR)

Inspire ID: 144382

Status: VALIDATED

Authors: - Peter Richardson

References: none listed

Beams: * *

Beam energies: ANY

Run details: none listed

Measurement of the mass spectrum for π⁺π⁻ in ψ(2S) → π⁺π⁻J/ψ decays by the MARK-II experiment.

Source code:`MARKII_1979_I144382.cc`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief psi(2S) -> J/psi pi+pi-
  class MARKII_1979_I144382 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(MARKII_1979_I144382);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(UnstableParticles(Cuts::pid == 100443), "UFS");
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1 + ix, 1, 1);
    }


    void findDecayProducts(const Particle& mother,
                           unsigned int& nstable,
                           Particles& pip,
                           Particles& pim,
                           Particles& onium) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == PID::PIMINUS) {
          pim.push_back(p);
          ++nstable;
        }
        else if (id == PID::PIPLUS) {
          pip.push_back(p);
          ++nstable;
        }
        else if (id == 443) {
          onium.push_back(p);
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, pip, pim, onium);
        }
        else {
          ++nstable;
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // loop over unstable particles
      for (const Particle& ups : apply<UnstableParticles>(event, "UFS").particles()) {
        unsigned int nstable(0);
        Particles pip, pim, onium;
        findDecayProducts(ups, nstable, pip, pim, onium);
        // check for onium
        if (onium.size() != 1 || nstable != 3 || pip.size() != 1 || pim.size() != 1) continue;
        double mpipi = (pip[0].momentum() + pim[0].momentum()).mass();
        _h[0]->fill(sqr(mpipi));
        double mpi = 2. * pip[0].mass();
        double x = (mpipi - mpi) / (ups.mass() - onium[0].mass() - mpi);
        _h[1]->fill(x);
      }
    }


    /// 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(MARKII_1979_I144382);

}

Rivet analyses

π+π− spectrum in ψ(2S) → π+π−J/ψ

Source code:MARKII_1979_I144382.cc

π⁺π⁻ spectrum in ψ(2S) → π⁺π⁻J/ψ

Source code:`MARKII_1979_I144382.cc`