Rivet analyses

title: CRYSTAL_BALL_1982_I168793

$\gamma\gamma\to \pi^0\pi^0$ for centre-of-mass energies between 0.72 and 1.8 GeV

Experiment: CRYSTAL_BALL (PEP)

Inspire ID: 168793

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 41 (1990) 3324, 1990

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons, pi0 must be set stable

Measurement of the differential cross section for $\gamma\gamma\to \pi^0\pi^0$ for $0.72 \text{GeV} < W < 1.8 \text{GeV}$. 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 kaon scattering angle are measured.

Source code:CRYSTAL_BALL_1982_I168793.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief Diphoton to hadrons at centre-of-mass energies between 0.72 and 1.8 GeV class CRYSTAL_BALL_1982_I168793 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CRYSTAL_BALL_1982_I168793);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  // histos
  if (inRange(sqrtS() / GeV, 0.72, 1.8)) {
    book(_mult, "TMP/mult", refData(1, 1, 1));
    if (inRange(sqrtS() / GeV, 1.04, 1.48)) book(_h_cTheta, 2, 1, 1);
  }
  else
    throw Error("Invalid CMS energy for CRYSTAL_BALL_1990_I294492");
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  Particles part = apply<FinalState>(event, "FS").particles();
  if (part.size() != 2) vetoEvent;
  for (const Particle& p : part) {
    if (p.pid() != PID::PI0) vetoEvent;
  }
  const double cTheta = abs(part[0].momentum().z() / part[0].momentum().p3().mod());
  if (cTheta <= 0.7) _mult->fill(sqrtS() / GeV);
  if (_h_cTheta) _h_cTheta->fill(cTheta);
}


/// Normalise histograms etc., after the run
void finalize() {
  const double fact = crossSection() / nanobarn / sumOfWeights();
  if (_h_cTheta) scale(_h_cTheta, fact);
  scale(_mult, fact);
  Estimate1DPtr tmp;
  book(tmp, 1, 1, 1);
  barchart(_mult, tmp);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _mult, _h_cTheta;
/// @}

};

RIVET_DECLARE_PLUGIN(CRYSTAL_BALL_1982_I168793);

} ```