Rivet analyses

title: MARKII_1984_I195739

$\gamma\gamma\to\pi^+\pi^-/K^+K^-$ for centre-of-mass energies between 1.6 and 2.5 GeV

Experiment: MARKII (PEP)

Inspire ID: 195739

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 30 (1984) 851, 1984

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-/K^+K^-$ for $1.6 \text{GeV} < W < 2.5 \text{GeV}$.

Source code:MARKII_1984_I195739.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> pi+pi-/K+ K- class MARKII_1984_I195739 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(MARKII_1984_I195739);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(FinalState(), "FS");
  // check CMS energy in range
  if (sqrtS() < 1.6 * GeV || sqrtS() > 2.5 * GeV)
    throw Error("Invalid CMS energy for MARKII_1984_I195739");
  book(_cPiK, "/TMP/nPiK_");
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  Particles part = apply<FinalState>(event, "FS").particles();
  if (part.size() != 2) vetoEvent;
  if (part[0].pid() != -part[1].pid()) vetoEvent;
  double cTheta(0.);
  bool foundPi(false), foundK(false);
  for (const Particle& p : part) {
    if (p.pid() == PID::PIPLUS) {
      foundPi = true;
      cTheta = abs(p.momentum().z() / p.momentum().p3().mod());
    }
    else if (p.pid() == PID::KPLUS) {
      foundK = true;
      cTheta = abs(p.momentum().z() / p.momentum().p3().mod());
    }
  }
  if (!foundPi && !foundK) vetoEvent;
  if (cTheta > 0.3) vetoEvent;
  _cPiK->fill();
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / nanobarn / sumOfWeights();
  double sigma = _cPiK->val() * fact;
  double error = _cPiK->err() * fact;
  Estimate1DPtr cross;
  book(cross, 1, 1, 1);
  for (auto& b : cross->bins()) {
    if (inRange(sqrtS(), b.xMin(), b.xMax())) {
      b.set(sigma, error);
    }
  }
}

///@}


/// @name Histograms
///@{
CounterPtr _cPiK;
///@}

};

RIVET_DECLARE_PLUGIN(MARKII_1984_I195739);

} ```