Rivet analyses

title: BELLE_2005_I677625

$\gamma\gamma\to p \bar{p}$ for centre-of-mass energies between 2.025 and 4.0 GeV

Experiment: BELLE (KEKB)

Inspire ID: 677625

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett.B 621 (2005) 41-55, 2005

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to p \bar{p}$ for $2.025 \text{GeV} < W < 4.0 \text{GeV}$. 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 proton scattering angle are measured.

Source code:BELLE_2005_I677625.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> p pbar class BELLE_2005_I677625 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2005_I677625);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  // book histos
  if (inRange(sqrtS() / GeV, 2.025, 4.)) {
    book(_sigmaProton, "TMP/nProton", refData(1, 1, 1));
    if (inRange(sqrtS() / GeV, 2.075, 2.9) || inRange(sqrtS() / GeV, 3.1, 4.)) {
      double sMin = 2.075, sMax = 2.1, step = 0.1;
      unsigned int ihist = 3, iy = 1;
      while (sMin < 4.) {
        if (inRange(sqrtS() / GeV, sMin, sMax)) break;
        sMin = sMax;
        sMax += step;
        iy += 1;
        if (iy == 4) {
          ihist += 1;
          iy = 1;
        }
        if (fuzzyEquals(2.9, sMin)) {
          sMin = 3.1;
          sMax = 3.5;
          step = 0.5;
        }
      }
      book(_h_cTheta[0], ihist, 1, iy);
    }
    if (inRange(sqrtS() / GeV, 2.075, 2.5)) {
      book(_h_cTheta[1], 2, 1, 1);
    }
    else if (inRange(sqrtS() / GeV, 2.5, 3.)) {
      book(_h_cTheta[1], 2, 1, 2);
    }
    else if (inRange(sqrtS() / GeV, 3., 4.)) {
      book(_h_cTheta[1], 2, 1, 3);
    }
  }
  else {
    throw Error("Invalid CMS energy for BELLE_2005_I677625");
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  Particles part = apply<FinalState>(event, "FS").particles();
  if (part.size() != 2) vetoEvent;
  double cTheta(0.);
  bool foundP(false), foundM(false);
  for (const Particle& p : part) {
    if (p.pid() == PID::PROTON) {
      foundP = true;
      cTheta = abs(p.mom().z() / p.mom().p3().mod());
    }
    else if (p.pid() == PID::ANTIPROTON) {
      foundM = true;
    }
  }
  if (!foundP || !foundM) vetoEvent;
  if (cTheta <= 0.6) _sigmaProton->fill(sqrtS());
  if (_h_cTheta[0]) _h_cTheta[0]->fill(cTheta);
  if (_h_cTheta[1]) _h_cTheta[1]->fill(cTheta);
}


/// Normalise histograms etc., after the run
void finalize() {
  const double fact = crossSection() / nanobarn / sumOfWeights();
  for (unsigned int ix = 0; ix < 2; ++ix) {
    if (_h_cTheta[ix]) scale(_h_cTheta[ix], fact);
  }
  scale(_sigmaProton, fact);
  Estimate1DPtr tmp;
  book(tmp, 1, 1, 1);
  barchart(_sigmaProton, tmp);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_cTheta[2];
Histo1DPtr _sigmaProton;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2005_I677625);

} ```