Rivet analyses

title: JADE_1990_I295180

$\gamma\gamma\to \pi^0\pi^0$ for centre-of-mass energies between 2.0 and 3.55 GeV

Experiment: JADE (PETRA)

Inspire ID: 295180

Status: UNVALIDATED

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 $2.0 \text{GeV} < W < 3.5 \text{GeV}$. Only the cross section as a function of the centre-of-mass energy of the photonic collision is implemented as the other distributions are unnormalised or not corrected.

Source code:JADE_1990_I295180.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> pi0pi0 class JADE_1990_I295180 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(JADE_1990_I295180);


/// @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, 2., 3.5)) {
    book(_npipi, "TMP/pipi", refData(1, 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 <= 0.3) _npipi->fill(sqrtS() / GeV);
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_npipi, crossSection() / nanobarn / sumOfWeights());
  Estimate1DPtr tmp;
  book(tmp, 1, 1, 1);
  barchart(_npipi, tmp);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(JADE_1990_I295180);

} ```