Rivet analyses

title: BELLE_2005_I667712

$\gamma\gamma\to\pi^+\pi^-$ and $K^+K^-$ for centre-of-mass energies between 2.4 and 4.1 GeV

Experiment: BELLE (KEKB)

Inspire ID: 667712

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett.B 615 (2005) 39-49

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-$ and $K^+K^-$ for $2.4 \text{GeV} < W < 4.1 \text{GeV}$. 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 pion scattering angle are measured.

Source code:BELLE_2005_I667712.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// gamma gamma -> pi+pi-/K+ K- for energies between 2.4 and 4.1 GeV class BELLE_2005_I667712 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2005_I667712);


/// @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() < 2.4 * GeV || sqrtS() > 4.1 * GeV)
    throw Error("Invalid CMS energy for BELLE_2005_I667712");
  for (unsigned int ix = 0; ix < 7; ++ix) {
    std::ostringstream title;
    title << "/TMP/nPi_" << ix;
    book(_cPi[ix], title.str());
  }
  for (unsigned int ix = 0; ix < 7; ++ix) {
    std::ostringstream title;
    title << "/TMP/nK_" << ix;
    book(_cK[ix], title.str());
  }
}


/// 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;
  int ibin = cTheta / 0.1;
  if (ibin > 5) vetoEvent;
  if (foundPi) {
    _cPi[0]->fill();
    _cPi[ibin + 1]->fill();
  }
  else if (foundK) {
    _cK[0]->fill();
    _cK[ibin + 1]->fill();
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / nanobarn / sumOfWeights();
  for (unsigned int ip = 0; ip < 2; ++ip) {
    CounterPtr denom = ip == 0 ? _cPi[0] : _cK[0];
    if (denom->numEntries() == 0) continue;
    for (unsigned int ih = 0; ih < 7; ++ih) {
      CounterPtr numer = ip == 0 ? _cPi[ih] : _cK[ih];
      double sigma = numer->val() * fact;
      double error = numer->err() * fact;
      // bin width for 2d dist
      if (ih != 0) {
        sigma /= 0.1;
        error /= 0.1;
      }
      unsigned int ix = 5 + ip, iy = ih;
      if (ih == 0) {
        ix = 1;
        iy = ip == 0 ? 2 : 1;
      }
      // ratio
      Estimate0D temp;
      Estimate1DPtr cross, ratio;
      book(cross, ix, 1, iy);
      if (ih != 0) {
        book(ratio, ix - 2, 1, iy);
        temp = *numer / *denom;
      }
      for (auto& b : cross->bins()) {
        if (inRange(sqrtS(), b.xMin(), b.xMax())) {
          b.set(sigma, error);
          if (ih != 0) {
            ratio->bin(b.index()).set(temp.val() / 0.1, temp.errPos() / 0.1);
          }
        }
      }
    }
  }
}

///@}


/// @name Histograms
///@{
CounterPtr _cPi[7], _cK[7];
///@}

};

RIVET_DECLARE_PLUGIN(BELLE_2005_I667712);

} ```