Rivet analyses

γγ → pp̄ 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 γγ → pp̄ for 2GeV < W < 2.8GeV. 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++ -*-
#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);

}