Rivet analyses

title: TPC_1987_I246557

$\gamma\gamma\to p \bar{p}$ for centre-of-mass energies between 2 and 2.8 GeV

Experiment: TPC (PEP)

Inspire ID: 246557

Status: UNVALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 36 (1987) 3506

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 $2 \text{GeV} < W < 2.8\text{GeV}$. 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:TPC_1987_I246557.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> p pbar class TPC_1987_I246557 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(TPC_1987_I246557);


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

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

  if (!inRange(sqrtS() / GeV, 2.0, 2.8)) raiseBeamErrorIf(true);

  // book histos
  book(_h_cTheta1, 3, 1, 1);
  book(_h_cTheta2, 3, 1, 2);
  book(_cProton, 1, 1, 1);

  // Determine which sqrtS bin needs to be filled
  for (const string& edge : _cProton.binning().edges<0>()) {
    if (isCompatibleWithSqrtS(stod(edge) * GeV)) {
      _edge = edge;
      break;
    }
  }
}


/// 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.momentum().z() / p.momentum().p3().mod());
    }
    else if (p.pid() == PID::ANTIPROTON)
      foundM = true;
  }
  if (!foundP || !foundM) vetoEvent;
  if (cTheta <= 0.6) _cProton->fill(_edge);
  if (sqrtS() <= 2.8) {
    (inRange(sqrtS() / GeV, 2.1, 2.4) ? _h_cTheta1 : _h_cTheta2)->fill(cTheta);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  const double fact = crossSection() / nanobarn / sumOfWeights();
  scale(_h_cTheta1, fact);
  scale(_h_cTheta2, fact);
  scale(_cProton, fact);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_cTheta1, _h_cTheta2;
BinnedHistoPtr<string> _cProton;
string _edge = "OTHER"s;
/// @}

};

RIVET_DECLARE_PLUGIN(TPC_1987_I246557);

} ```