Rivet analyses

title: CUSB_1984_I199809

Pion Mass Spectrum in $\Upsilon(2S)\to\Upsilon(1S)\pi^+\pi^-$

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 $\pi^+\pi^-$ mass Spectrum in $\Upsilon(2S)\to\Upsilon(1S)\pi^+\pi^-$ decays.

Source code:CUSB_1984_I199809.cc

```c++ // -- 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);

} ```