Rivet analyses

title: TASSO_1983_I191417

$\gamma\gamma\to p \bar{p}$ for centre-of-mass energies between 2 and 3.1 GeV

Experiment: TASSO (PETRA)

Inspire ID: 191417

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett.B 130 (1983) 449-453

Beams: 22 22

Beam energies: (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.3, 1.3); (1.4, 1.4); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5)GeV

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to p \bar{p}$ for $2 \text{GeV} < W < 3.1 \text{GeV}$. 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 proton scattering angle are measured.

Source code:TASSO_1983_I191417.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> p pbar class TASSO_1983_I191417 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(TASSO_1983_I191417);


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

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

  // book histos
  book(_h["cProton"], 1, 1, 1);
  book(_h["cTheta1"], 2, 1, 1);
  book(_h["cTheta2"], 2, 1, 2);
  for (const string& en : _h["cProton"].binning().edges<0>()) {
    if (isCompatibleWithSqrtS(stod(en) * GeV)) {
      _sqs = en;
      break;
    }
  }
  raiseBeamErrorIf(_sqs.empty());
  _axis = YODA::Axis<double>({0., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7});
  _edges = _h["cTheta2"].binning().edges<0>();
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const 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) _h["cProton"]->fill(_sqs);
  if (sqrtS() <= 2.8) {
    const size_t idx = _axis.index(cTheta);
    if (0 < idx && idx < _axis.numBins()) {
      _h[sqrtS() > 2.4 ? "cTheta2"s : "cTheta1"s]->fill(_edges[idx - 1]);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h, crossSection() / nanobarn / sumOfWeights());
  for (const string& label : vector<string>{"cTheta1"s, "cTheta2"s}) {
    for (auto& b : _h[label]->bins()) {
      const size_t idx = b.index();
      b.scaleW(1. / _axis.width(idx));
    }
  }
}

/// @}


/// @name Histograms
/// @{
map<string, BinnedHistoPtr<string>> _h;
string _sqs = "";
vector<string> _edges;
YODA::Axis<double> _axis;
/// @}

};

RIVET_DECLARE_PLUGIN(TASSO_1983_I191417); } ```