Rivet analyses

title: TPC_1986_I228072

$\gamma\gamma\to\pi^+\pi^-$ ($0.5<\sqrt{s}<3.25$ GeV) and $K^+K^-$ ($1.25<\sqrt{s}<3.5$ GeV)

Experiment: TPC (PEP)

Inspire ID: 228072

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 57 (1986) 404, 1986

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-$ ($0.5<\sqrt{s}<3.25$ GeV) and $K^+K^-$ ($1.25<\sqrt{s}<3.5$ GeV). The cross section as a function of the centre-of-mass energy of the photonic collision is measured

Source code:TPC_1986_I228072.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/LeptonFinder.hh"

include "Rivet/Projections/MissingMomentum.hh"

include "Rivet/Projections/PromptFinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> pi+pi-/K+ K- class TPC_1986_I228072 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(TPC_1986_I228072);


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

/// Book histograms and initialise projections before the run
void init() {
  // Final state
  declare(FinalState(), "FS");

  // Check CMS energy in range
  if (sqrtS() < 0.5 * GeV || sqrtS() > 3.5 * GeV) throw Error("Invalid CMS energy for TPC_1986_I228072");

  // Book histograms
  book(_cPi[0], "/TMP/nPi_06");
  book(_cPi[1], "/TMP/nPi_03");
  book(_cK, "/TMP/nK");
}


/// 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 > 0.6) vetoEvent;
  if (foundPi) {
    _cPi[0]->fill();
    if (cTheta < 0.3) _cPi[1]->fill();
  }
  else if (foundK)
    _cK->fill();
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / nanobarn / sumOfWeights();
  for (unsigned int ih = 1; ih < 6; ++ih) {
    if (ih == 2 || ih == 3) continue;
    double sigma(0.), error(0.);
    CounterPtr count;
    if (ih == 1) {
      count = _cPi[0];
    }
    else if (ih == 4) {
      count = _cPi[1];
    }
    else if (ih == 5) {
      count = _cK;
    }
    else
      assert(false);
    if (count->numEntries() == 0) continue;
    sigma = count->val() * fact;
    error = count->err() * fact;
    Estimate1DPtr cross;
    book(cross, ih, 1, 1);
    for (auto& b : cross->bins()) {
      if (inRange(sqrtS(), b.xMin(), b.xMax())) {
        b.set(sigma, error);
      }
    }
  }
}

///@}


/// @name Histograms
///@{
CounterPtr _cPi[2], _cK;
///@}

};

RIVET_DECLARE_PLUGIN(TPC_1986_I228072);

} ```