Rivet analyses

title: CRYSTAL_BALL_1991_I297905

$\pi^0$ and $\eta$ spectra for $e^+e^-$ collisions in the continuum and at $\Upsilon(1S)$

Experiment: CRYSTAL_BALL (DORIS)

Inspire ID: 297905

Status: UNVALIDATED

Authors: - Peter Richardson

References: - Z.Phys.C 49 (1991) 225-234

Beams: e- e+

Beam energies: (4.7, 4.7)GeV

Run details: - $e^+ e^-$ analysis near the $\Upsilon$ resonances

Measurement of the inclusive production of the $\pi^0$ and $\eta$ mesons in $e^+e^-$ annihilation in the Upsilon region. Data are taken on the $\Upsilon(1S)$ and in the nearby continuum.

Source code:CRYSTAL_BALL_1991_I297905.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief pi0 and eta at Upsilon 1 and continuum class CRYSTAL_BALL_1991_I297905 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CRYSTAL_BALL_1991_I297905);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  // Book histograms
  book(_h_cont_pi[0], 3, 1, 1);
  book(_h_cont_pi[1], 3, 1, 2);
  book(_h_ups1_pi, 4, 1, 1);
  book(_h_cont_eta[0], 5, 1, 1);
  book(_h_cont_eta[1], 5, 1, 2);
  book(_h_ups1_eta, 6, 1, 1);
  // counters
  book(_n_Cont[0], 1, 1, 1);
  book(_n_Cont[1], 1, 1, 2);
  book(_n_Ups[0], 2, 1, 1);
  book(_n_Ups[1], 2, 1, 2);
  book(_weightSum_cont, "/TMP/weightSum_cont");
  book(_weightSum_Ups1, "/TMP/weightSum_Ups1");
}

/// Recursively walk the decay tree to find decay products of @a p
void findDecayProducts(Particle mother, Particles& unstable) {
  for (const Particle& p : mother.children()) {
    const int id = p.pid();
    if (id == 111 or id == 221) {
      unstable.push_back(p);
    }
    if (!p.children().empty()) {
      findDecayProducts(p, unstable);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // Find the Upsilons among the unstables
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  Particles upsilons = ufs.particles(Cuts::pid == 553);
  // Continuum
  if (upsilons.empty()) {
    MSG_DEBUG("No Upsilons found => continuum event");
    _weightSum_cont->fill();
    unsigned int npi0(0), neta(0);
    for (const Particle& p : ufs.particles(Cuts::pid == 111 or Cuts::pid == 221)) {
      const int id = p.pid();
      const double xp = 2. * p.E() / sqrtS();
      const double beta = p.p3().mod() / p.E();
      if (id == 111) {
        ++npi0;
        for (unsigned int ix = 0; ix < 2; ++ix) {
          _h_cont_pi[ix]->fill(xp, 1. / beta);
        }
      }
      else {
        ++neta;
        for (unsigned int ix = 0; ix < 2; ++ix) {
          _h_cont_eta[ix]->fill(xp, 1. / beta);
        }
      }
    }
    _n_Cont[0]->fill(sqrtS(), npi0);
    _n_Cont[1]->fill(sqrtS(), neta);
  }
  // Upsilon(s) found
  else {
    MSG_DEBUG("Upsilons found => resonance event");
    for (const Particle& ups : upsilons) {
      _weightSum_Ups1->fill();
      Particles unstable;
      // Find the decay products we want
      findDecayProducts(ups, unstable);
      LorentzTransform cms_boost;
      if (ups.p3().mod() > 1 * MeV) {
        cms_boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
      }
      const double mass = ups.mass();
      // loop over decay products
      for (const Particle& p : unstable) {
        const int id = p.pid();
        const FourMomentum p2 = cms_boost.transform(p.momentum());
        const double xp = 2. * p2.E() / mass;
        const double beta = p2.p3().mod() / p2.E();
        if (id == 111) {
          _n_Ups[0]->fill(Ecm);
          _h_ups1_pi->fill(xp, 1. / beta);
        }
        else if (id == 221) {
          _n_Ups[1]->fill(Ecm);
          _h_ups1_eta->fill(xp, 1. / beta);
        }
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // Scale histos
  if (_weightSum_cont->val() > 0.) {
    scale(_h_cont_pi[0], 1. / *_weightSum_cont);
    scale(_h_cont_pi[1], sqr(sqrtS()) * crossSection() / microbarn / sumOfWeights());
    scale(_h_cont_eta[0], 1. / *_weightSum_cont);
    scale(_h_cont_eta[1], sqr(sqrtS()) * crossSection() / microbarn / sumOfWeights());
  }
  if (_weightSum_Ups1->val() > 0.) {
    scale(_h_ups1_pi, 1. / *_weightSum_Ups1);
    scale(_h_ups1_eta, 1. / *_weightSum_Ups1);
    scale(_n_Ups[0], 1. / *_weightSum_Ups1);
    scale(_n_Ups[1], 1. / *_weightSum_Ups1);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_cont_pi[2], _h_ups1_pi;
Histo1DPtr _h_cont_eta[2], _h_ups1_eta;
BinnedHistoPtr<string> _n_Ups[2];
Profile1DPtr _n_Cont[2];
CounterPtr _weightSum_cont, _weightSum_Ups1;
const string Ecm = "9.8";
/// @}

};

RIVET_DECLARE_PLUGIN(CRYSTAL_BALL_1991_I297905);

} ```