Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/DISKinematics.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {


  /// @brief ZEUS dijet photoproduction study used in the ZEUS jets PDF fit
  ///
  /// This class is a reproduction of the HZTool routine for the ZEUS
  /// dijet photoproduction paper which was used in the ZEUS jets PDF fit.
  ///
  /// @note Cleaning cuts on event pT/sqrt(Et) and y_e are not needed in MC analysis.
  ///
  /// @author Andy Buckley
  /// @author Ilkka Helenius
  class ZEUS_2001_I568665 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ZEUS_2001_I568665);


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

    // Book projections and histograms
    void init() {

      // Projections
      /// @todo Acceptance
      // checking recombination scheme and radius checked with original code from M.Wing
      FinalState fs;
      declare(FastJets(fs, fastjet::JetAlgorithm::kt_algorithm, fastjet::RecombinationScheme::Et_scheme, 1.0),
              "Jets");
      declare(DISKinematics(), "Kinematics");

      // Table 1
      book(_h_costh[0], 1, 1, 1);
      book(_h_costh[1], 1, 1, 2);
      // Table 2
      book(_h_etjet1[1][0], 2, 1, 1);
      book(_h_etjet1[1][1], 3, 1, 1);
      book(_h_etjet1[1][2], 4, 1, 1);
      book(_h_etjet1[1][3], 5, 1, 1);
      book(_h_etjet1[1][4], 6, 1, 1);
      book(_h_etjet1[1][5], 7, 1, 1);
      // Table 3
      book(_h_etjet1[0][0], 8, 1, 1);
      book(_h_etjet1[0][1], 9, 1, 1);
      book(_h_etjet1[0][2], 10, 1, 1);
      book(_h_etjet1[0][3], 11, 1, 1);
      book(_h_etjet1[0][4], 12, 1, 1);
      book(_h_etjet1[0][5], 13, 1, 1);
      // Table 4
      book(_h_etajet2[1][0], 14, 1, 1);
      book(_h_etajet2[1][1], 15, 1, 1);
      book(_h_etajet2[1][2], 16, 1, 1);
      // Table 5
      book(_h_etajet2[0][0], 17, 1, 1);
      book(_h_etajet2[0][1], 18, 1, 1);
      book(_h_etajet2[0][2], 19, 1, 1);
      // Table 6
      book(_h_xobsy[0], 20, 1, 1);
      book(_h_xobsy[1], 21, 1, 1);
      book(_h_xobsy[2], 22, 1, 1);
      book(_h_xobsy[3], 23, 1, 1);
    }


    // Do the analysis
    void analyze(const Event& event) {

      // Determine kinematics, including event orientation since ZEUS coord system is for +z = proton direction
      const DISKinematics& kin = apply<DISKinematics>(event, "Kinematics");
      if (kin.failed()) vetoEvent;
      const int orientation = kin.orientation();

      // Q2 and inelasticity cuts
      if (kin.Q2() > 1 * GeV2) vetoEvent;
      if (!inRange(kin.y(), 0.2, 0.85)) vetoEvent;

      // Jet selection
      const Jets jets = apply<FastJets>(event, "Jets")
                            .jets(Cuts::Et > 11 * GeV && Cuts::etaIn(-1 * orientation, 2.4 * orientation),
                                  cmpMomByEt);
      MSG_DEBUG("Jet multiplicity = " << jets.size());
      if (jets.size() < 2) vetoEvent;
      const Jet& j1 = jets[0];
      const Jet& j2 = jets[1];
      if (j1.Et() < 14 * GeV) vetoEvent;

      // Jet eta and cos(theta*) computation
      const double eta1 = orientation * j1.eta(), eta2 = orientation * j2.eta();
      const double etabar = (eta1 + eta2) / 2;
      const double etadiff = eta1 - eta2;
      const double costhetastar = tanh(etadiff / 2);

      // Computation of x_y^obs
      /// @note Assuming Ee is the lab frame positron momentum, not in proton rest frame cf. the ambiguous phrase in the paper
      const double xyobs = (j1.Et() * exp(-eta1) + j2.Et() * exp(-eta2))
          / (2 * kin.y() * kin.beamLepton().E());
      const size_t i_xyobs = (xyobs < 0.75) ? 0 : 1;

      // Calculate the invariant mass of the dijet as in the paper
      const double mjj = sqrt(2. * j1.Et() * j2.Et()
                              * (cosh(j1.eta() - j2.eta()) - cos(j1.phi() - j2.phi())));

      // Fill histograms
      // T1
      if (mjj > 42 * GeV && inRange(etabar, 0.1, 1.3)) _h_costh[i_xyobs]->fill(abs(costhetastar));
      // T2, T3: Symmetrize eta selection, each event contribute twice to the cross section
      for (size_t isel = 0; isel < 2; ++isel) {
        double etaJet1 = (isel == 0) ? orientation * j1.eta() : orientation * j2.eta();
        double etaJet2 = (isel == 0) ? orientation * j2.eta() : orientation * j1.eta();
        if (inRange(etaJet1, -1, 0) && inRange(etaJet2, -1, 0))
          _h_etjet1[i_xyobs][0]->fill(j1.Et() / GeV);
        else if (inRange(etaJet1, 0, 1) && inRange(etaJet2, -1, 0))
          _h_etjet1[i_xyobs][1]->fill(j1.Et() / GeV);
        else if (inRange(etaJet1, 0, 1) && inRange(etaJet2, 0, 1))
          _h_etjet1[i_xyobs][2]->fill(j1.Et() / GeV);
        else if (inRange(etaJet1, 1, 2.4) && inRange(etaJet2, -1, 0))
          _h_etjet1[i_xyobs][3]->fill(j1.Et() / GeV);
        else if (inRange(etaJet1, 1, 2.4) && inRange(etaJet2, 0, 1))
          _h_etjet1[i_xyobs][4]->fill(j1.Et() / GeV);
        else if (inRange(etaJet1, 1, 2.4) && inRange(etaJet2, 1, 2.4))
          _h_etjet1[i_xyobs][5]->fill(j1.Et() / GeV);
        // T4, T5
        if (inRange(etaJet1, -1, 0))
          _h_etajet2[i_xyobs][0]->fill(etaJet2);
        else if (inRange(etaJet1, 0, 1))
          _h_etajet2[i_xyobs][1]->fill(etaJet2);
        else if (inRange(etaJet1, 1, 2.4))
          _h_etajet2[i_xyobs][2]->fill(etaJet2);
      }
      // T6
      if (inRange(j1.Et() / GeV, 14, 17))
        _h_xobsy[0]->fill(xyobs);
      else if (inRange(j1.Et() / GeV, 17, 25))
        _h_xobsy[1]->fill(xyobs);
      else if (inRange(j1.Et() / GeV, 25, 35))
        _h_xobsy[2]->fill(xyobs);
      else if (inRange(j1.Et() / GeV, 35, 90))
        _h_xobsy[3]->fill(xyobs);
    }


    // Finalize
    void finalize() {
      const double sf = crossSection() / picobarn / sumOfWeights();
      for (size_t ix = 0; ix < 2; ++ix) {
        scale(_h_costh[ix], sf);
        for (auto& h : _h_etjet1[ix]) scale(h, sf);
        for (auto& h : _h_etajet2[ix]) scale(h, sf);
      }
      for (auto& h : _h_xobsy) scale(h, sf);
    }

    /// @}


  private:

    /// @name Histograms
    /// @{
    Histo1DPtr _h_costh[2], _h_etjet1[2][6], _h_etajet2[2][3], _h_xobsy[4];
    /// @}
  };


  RIVET_DECLARE_ALIASED_PLUGIN(ZEUS_2001_I568665, ZEUS_2001_S4815815);

}