Rivet analyses

title: CLEO_1994_I358510

$\gamma\gamma\to p \bar{p}$ for centre-of-mass energies between 2 and 3.25 GeV

Experiment: CLEO (CESR)

Inspire ID: 358510

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 50 (1994) 5484-5490, 1994

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to p \bar{p}$ for $2 \text{GeV} < W < 3.25 \text{GeV}$. Both the cross section as a function of the centre-of-mass energy of the photonic collision, and the differential cross section with respect to the proton scattering angle are measured.

Source code:CLEO_1994_I358510.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> p pbar class CLEO_1994_I358510 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_1994_I358510);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  // book histos
  if (inRange(sqrtS() / GeV, 2., 3.25)) {
    if (sqrtS() <= 2.5) {
      book(_h_cTheta, 2, 1, 1);
    }
    else if (sqrtS() <= 3.) {
      book(_h_cTheta, 3, 1, 1);
    }
    book(_cProton, "TMP/sigma", refData(1, 1, 1));
  }
  else {
    throw Error("Invalid CMS energy for CLEO_1994_I358510");
  }
  _axis = YODA::Axis<double>({0., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6});
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_h_cTheta && _edges.empty()) _edges = _h_cTheta->xEdges();
  Particles part = apply<FinalState>(event, "FS").particles();
  if (part.size() != 2) vetoEvent;
  double cTheta(0.);
  bool foundP(false), foundM(false);
  for (const Particle& p : part) {
    if (p.pid() == PID::PROTON) {
      foundP = true;
      cTheta = abs(p.momentum().z() / p.momentum().p3().mod());
    }
    else if (p.pid() == PID::ANTIPROTON) {
      foundM = true;
    }
  }
  if (!foundP || !foundM) vetoEvent;
  if (cTheta <= 0.6) _cProton->fill(sqrtS() / GeV);
  if (_h_cTheta) _h_cTheta->fill(disc(cTheta));
}


string disc(const double value) const {
  size_t idx = _axis.index(value);
  if (0 < idx && idx <= _axis.numBins()) return _edges[idx - 1];
  return "OTHER"s;
}


/// Normalise histograms etc., after the run
void finalize() {
  const double fact = crossSection() / nanobarn / sumOfWeights();
  if (_h_cTheta) {
    scale(_h_cTheta, fact);
    for (auto& b : _h_cTheta->bins()) {
      const size_t idx = b.index();
      b.scaleW(1. / _axis.width(idx));
    }
  }
  scale(_cProton, fact);
  Estimate1DPtr tmp;
  book(tmp, 1, 1, 1);
  barchart(_cProton, tmp);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h_cTheta;
Histo1DPtr _cProton;
YODA::Axis<double> _axis;
vector<string> _edges;
/// @}

};

RIVET_DECLARE_PLUGIN(CLEO_1994_I358510);

} ```