Rivet analyses

γγ → pp̄ 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 γγ → pp̄ for 2.025GeV < W < 4.0GeV. 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++ -*-
#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);

}