Rivet analyses

Pion Mass Spectrum in Υ(2S) → Υ(1S)π+π−

Experiment: CUSB (CESR)

Inspire ID: 199809

Status: VALIDATED

Authors: - Peter Richardson

References: - Nucl.Phys. B242 (1984) 31-50

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon(2S), original e+e-

Measurement of the π+π− mass Spectrum in Υ(2S) → Υ(1S)π+π− decays.

Source code:CUSB_1984_I199809.cc

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

namespace Rivet {


  /// @brief Upsilon(2S) -> Upsilon(1S) pi+pi-
  class CUSB_1984_I199809 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CUSB_1984_I199809);


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

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

      // Initialise and register projections
      declare(UnstableParticles(), "UFS");
      book(_hist, 1, 1, 1);
    }

    void findDecayProducts(const Particle& mother,
                           unsigned int& nstable,
                           Particles& pip,
                           Particles& pim,
                           Particles& pi0,
                           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 == PID::PI0) {
          pi0.push_back(p);
          ++nstable;
        }
        else if (abs(id) % 1000 == 443 || abs(id) % 1000 == 553) {
          onium.push_back(p);
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, pip, pim, pi0, 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(Cuts::pid == 100553)) {
        unsigned int nstable(0);
        Particles pip, pim, pi0, onium;
        findDecayProducts(ups, nstable, pip, pim, pi0, onium);
        // check for onium
        if (onium.size() != 1 || onium[0].pid() != 553 || nstable != 3) continue;
        // check for pipi
        if (!(pip.size() == 1 && pim.size() == 1)) continue;
        FourMomentum q = pip[0].momentum() + pim[0].momentum();
        _hist->fill(q.mass() / MeV);
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _hist;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CUSB_1984_I199809);

}