Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Event.hh"
#include "Rivet/Math/LorentzTrans.hh"
#include "Rivet/Particle.hh"
#include "Rivet/Projections/ChargedLeptons.hh"
#include "Rivet/Projections/LeptonFinder.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/MissingMomentum.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/InvisibleFinalState.hh"

namespace Rivet {


  /// @brief Measurement of W/gamma differential cross sections at sqrt(s) = 13 TeV
  class CMS_2021_I1978840 : public Analysis {
  public:

    struct WGammaRivetVariables {
      bool is_wg_gen;

      double l0_pt;
      double l0_eta;
      double l0_phi;
      double l0_M;
      int l0_q;
      unsigned l0_abs_pdgid;

      double p0_pt;
      double p0_eta;
      double p0_phi;
      double p0_M;
      bool p0_frixione;
      double p0_frixione_sum;

      double l0p0_dr;
      double mt_cluster;

      double n0_pt;
      double n0_eta;
      double n0_phi;
      double n0_M;

      double met_pt;
      double met_phi;

      double true_phi;
      double true_phi_f;

      int n_jets;

      WGammaRivetVariables() { resetVars(); }

      void resetVars() {
        is_wg_gen = false;
        l0_pt = 0.;
        l0_eta = 0.;
        l0_phi = 0.;
        l0_M = 0.;
        l0_q = 0;
        l0_abs_pdgid = 0;
        p0_pt = 0.;
        p0_eta = 0.;
        p0_phi = 0.;
        p0_M = 0.;
        p0_frixione = false;
        n0_pt = 0.;
        n0_eta = 0.;
        n0_phi = 0.;
        n0_M = 0.;
        met_pt = 0.;
        met_phi = 0.;
        true_phi = 0.;
        true_phi_f = 0.;
        l0p0_dr = 0.;
        mt_cluster = 0.;
        n_jets = 0;
      }
    };

    struct WGSystem {
      int lepton_charge;

      FourMomentum wg_system;

      FourMomentum c_w_boson;
      FourMomentum c_charged_lepton;
      FourMomentum c_neutrino;
      FourMomentum c_photon;

      FourMomentum r_w_boson;
      FourMomentum r_charged_lepton;
      FourMomentum r_neutrino;
      FourMomentum r_photon;

      WGSystem(Particle const& lep, FourMomentum const& neu, Particle const& pho, bool verbose);

      double phi();
      double symphi();
    };

    double photon_iso_dr_ = 0.4;
    double lepton_pt_cut_ = 30.;
    double lepton_abs_eta_cut_ = 2.5;
    double photon_pt_cut_ = 30.;
    double photon_abs_eta_cut_ = 2.5;
    double missing_pt_cut_ = 40.;
    double lepton_photon_dr_cut_ = 0.7;
    double dressed_lepton_cone_ = 0.1;

    double eft_lepton_pt_cut_ = 80.;
    double eft_photon_pt_cut_ = 150.;

    double jet_pt_cut_ = 30.;
    double jet_abs_eta_cut_ = 2.5;
    double jet_dr_cut_ = 0.4;

    WGammaRivetVariables vars_;
    map<string, Histo1DPtr> _h;


    RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2021_I1978840);


    void init() {
      vars_.resetVars();

      FinalState fs;
      declare(fs, "FinalState");

      // Jets - all final state particles excluding neutrinos
      VetoedFinalState vfs;
      vfs.vetoNeutrinos();
      FastJets fastjets(vfs, JetAlg::ANTIKT, 0.4);
      declare(fastjets, "Jets");

      // Dressed leptons
      ChargedLeptons charged_leptons(fs);
      PromptFinalState prompt_leptons(charged_leptons);
      declare(prompt_leptons, "PromptLeptons");

      IdentifiedFinalState photons(fs);
      photons.acceptIdPair(PID::PHOTON);
      PromptFinalState prompt_photons(photons);
      prompt_photons.acceptMuonDecays(true);
      prompt_photons.acceptTauDecays(true);

      LeptonFinder dressed_leptons(prompt_leptons, prompt_photons, dressed_lepton_cone_);
      declare(dressed_leptons, "LeptonFinder");

      // Photons
      VetoedFinalState vetoed_prompt_photons(prompt_photons);
      vetoed_prompt_photons.addVetoOnThisFinalState(dressed_leptons);
      declare(vetoed_prompt_photons, "Photons");

      // Invisibles
      InvisibleFinalState invisibles(OnlyPrompt::YES, TauDecaysAs::PROMPT, MuDecaysAs::PROMPT);
      declare(invisibles, "Invisibles");

      // MET
      declare(MissingMomentum(fs), "MET");

      // Booking of histograms
      book(_h["baseline_photon_pt"], 1, 1, 1);
      book(_h["baseline_photon_eta"], 8, 1, 1);
      book(_h["baseline_leppho_dr"], 15, 1, 1);
      book(_h["baseline_leppho_deta"], 22, 1, 1);
      book(_h["baseline_mt_cluster"], 29, 1, 1);
      book(_h["baseline_njet"], 36, 1, 1);
      book(_h["raz_leppho_deta"], 40, 1, 1);
      book(_h["eft_photon_pt_phi_0"], 54, 1, 1);
      book(_h["eft_photon_pt_phi_1"], 55, 1, 1);
      book(_h["eft_photon_pt_phi_2"], 56, 1, 1);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      vars_.resetVars();

      const Particles leptons = apply<FinalState>(event, "LeptonFinder").particlesByPt();

      if (leptons.size() == 0) {
        vetoEvent;
      }
      auto l0 = leptons.at(0);

      const Particles photons = apply<FinalState>(event, "Photons")
        .particlesByPt(DeltaRGtr(l0, lepton_photon_dr_cut_));
      if (photons.size() == 0) {
        vetoEvent;
      }
      auto p0 = photons.at(0);


      const Particles invisibles = apply<FinalState>(event, "Invisibles").particlesByPt();
      FourMomentum n0;
      for (auto const& inv : invisibles) {
        n0 += inv.momentum();
      }

      if (invisibles.size() == 0) {
        vetoEvent;
      }

      FourMomentum met = apply<MissingMomentum>(event, "MET").missingMomentum();
      // Redefine the MET
      met = FourMomentum(met.pt(), met.px(), met.py(), 0.);

      // Filter jets on pT, eta and DR with lepton and photon
      Jets jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > jet_pt_cut_ && Cuts::abseta < jet_abs_eta_cut_);
      idiscard(jets, deltaRLess(l0, jet_dr_cut_));
      idiscard(jets, deltaRLess(p0, jet_dr_cut_));

      if (leptons.size() >= 1 && photons.size() >= 1 && invisibles.size() >= 1) {
        // Populate variables
        vars_.is_wg_gen = true;
        vars_.l0_pt = l0.pt()/GeV;
        vars_.l0_eta = l0.eta();
        vars_.l0_phi = l0.phi(PhiMapping::MINUSPI_PLUSPI);
        vars_.l0_M = l0.mass()/GeV;
        vars_.l0_q = l0.charge();
        vars_.l0_abs_pdgid = l0.abspid();
        vars_.p0_pt = p0.pt()/GeV;
        vars_.p0_eta = p0.eta();
        vars_.p0_phi = p0.phi(PhiMapping::MINUSPI_PLUSPI);
        vars_.p0_M = p0.mass()/GeV;
        vars_.n_jets = jets.size();
        vars_.l0p0_dr = deltaR(l0, p0);
        vars_.n0_pt = n0.pt()/GeV;
        vars_.n0_eta = n0.eta();
        vars_.n0_phi = n0.phi(PhiMapping::MINUSPI_PLUSPI);
        vars_.n0_M = n0.mass()/GeV;
        vars_.met_pt = met.pt()/GeV;
        vars_.met_phi = met.phi(PhiMapping::MINUSPI_PLUSPI);

        // Here we build a list of particles to cluster jets, to be used in the photon isolation.
        // The selection of particles that we want to veto from this isolation sum is non-trivial:
        // the leading pT lepton, the leading pT photon that has DeltaR > 0.7 from the leading pT
        // lepton, the invisibles  and any tau decay products. Therefore, the selection is done
        // here instead of in the initialise method.
        Particles finalparts_iso = apply<FinalState>(event, "FinalState").particles();
        Particles filtered_iso;
        for (Particle const& p : finalparts_iso) {
          bool veto_particle = false;
          if (p.genParticle() == l0.genParticle() || p.genParticle() == p0.genParticle() || p.fromTau()) {
            veto_particle = true;
          }
          for (auto const& inv : invisibles) {
            if (p.genParticle() == inv.genParticle()) {
              veto_particle = true;
            }
          }
          if (!veto_particle) {
            filtered_iso.push_back(p);
          }
        }
        auto proj = getProjection<FastJets>("Jets");
        proj.reset();
        proj.calc(filtered_iso);
        auto jets_iso = proj.jets();

        vars_.p0_frixione = true;
        double frixione_sum = 0.;

        // Apply Frixione isolation to the photon:
        auto jparts = sortBy(jets_iso, [&](Jet const& part1, Jet const& part2) {
          return deltaR(part1, p0) < deltaR(part2, p0);
        });

        for (auto const& ip : jparts) {
          double dr = deltaR(ip, p0);
          if (dr >= photon_iso_dr_) {
            break;
          }
          frixione_sum += ip.pt();
          if (frixione_sum > (p0.pt() * ((1. - cos(dr)) / (1. - cos(photon_iso_dr_))))) {
            vars_.p0_frixione = false;
          }
        }

        // Now calculate EFT phi observables
        auto wg_system = WGSystem(l0, n0, p0, false);

        vars_.true_phi = wg_system.phi();
        vars_.true_phi_f = wg_system.symphi();

        // Calculate mTcluster
        auto cand1 = l0.momentum() + p0.momentum();
        auto full_system = cand1 + met;
        double mTcluster2 = sqr(sqrt(cand1.mass2() + cand1.pt2()) + met.pt()) - full_system.pt2();
        if (mTcluster2 > 0) {
          vars_.mt_cluster = sqrt(mTcluster2);
        } else {
          vars_.mt_cluster = 0.;
        }

        if (vars_.l0_pt > lepton_pt_cut_ && fabs(vars_.l0_eta) < lepton_abs_eta_cut_ &&
            vars_.p0_pt > photon_pt_cut_ && fabs(vars_.p0_eta) < photon_abs_eta_cut_ &&
            vars_.p0_frixione && vars_.l0p0_dr > lepton_photon_dr_cut_ &&
            vars_.met_pt > missing_pt_cut_) {
          _h["baseline_photon_pt"]->fill(vars_.p0_pt / GeV);
          _h["baseline_photon_eta"]->fill(vars_.p0_eta);
          _h["baseline_leppho_dr"]->fill(vars_.l0p0_dr);
          _h["baseline_leppho_deta"]->fill(vars_.l0_eta - vars_.p0_eta);
          _h["baseline_mt_cluster"]->fill(vars_.mt_cluster / GeV);
          double fill_n_jets = vars_.n_jets >= 2 ? 2. : double(vars_.n_jets);
          _h["baseline_njet"]->fill(fill_n_jets);
          if (vars_.n_jets == 0 && vars_.mt_cluster > 150.) {
            _h["raz_leppho_deta"]->fill(vars_.l0_eta - vars_.p0_eta);
          }
        }

        if (vars_.l0_pt > eft_lepton_pt_cut_ && fabs(vars_.l0_eta) < lepton_abs_eta_cut_ &&
            vars_.p0_pt > eft_photon_pt_cut_ && fabs(vars_.p0_eta) < photon_abs_eta_cut_ &&
            vars_.p0_frixione && vars_.l0p0_dr > lepton_photon_dr_cut_ &&
            vars_.met_pt > missing_pt_cut_ && vars_.n_jets == 0) {
          double absphi = fabs(vars_.true_phi_f);
          if (absphi > 0. && absphi <= (PI / 6.)) {
            _h["eft_photon_pt_phi_0"]->fill(vars_.p0_pt / GeV);
          } else if (absphi > (PI / 6.) && absphi <= (PI / 3.)) {
            _h["eft_photon_pt_phi_1"]->fill(vars_.p0_pt / GeV);
          } else if (absphi > (PI / 3.) && absphi <= (PI / 2.)) {
            _h["eft_photon_pt_phi_2"]->fill(vars_.p0_pt / GeV);
          }
        }
      }
    }


    void finalize() {
      double flavor_factor = 3. / 2.;  // account for the fact that tau events are vetoed
      // Scale according to cross section
      for (string x :
             {"baseline_photon_pt", "baseline_photon_eta", "baseline_leppho_dr", "baseline_leppho_deta",
              "baseline_mt_cluster", "baseline_njet", "raz_leppho_deta", "eft_photon_pt_phi_0",
              "eft_photon_pt_phi_1", "eft_photon_pt_phi_2"}) {
        scale(_h[x], flavor_factor * crossSection() / femtobarn / sumOfWeights());
      }

      // Since these are really 2D, we need to divide by the y bin width:
      for (string x : {"eft_photon_pt_phi_0", "eft_photon_pt_phi_1", "eft_photon_pt_phi_2"}) {
        scale(_h[x], 1. / (PI / 6.));
      }
    }

  };


  CMS_2021_I1978840::WGSystem::WGSystem(Particle const& lep, FourMomentum const& neu,
                                        Particle const& pho, bool verbose) {
    lepton_charge = lep.charge3() / 3;
    wg_system += lep.momentum();
    wg_system += neu;
    wg_system += pho.momentum();

    if (verbose) {
      cout << "> charge:    " << lepton_charge << "\n";
      cout << "> wg_system: " << wg_system << "\n";
      cout << "> lepton   : " << lep.momentum() << "\n";
      cout << "> neutrino : " << neu << "\n";
      cout << "> photon   : " << pho.momentum() << "\n";
    }

    auto boost = LorentzTransform::mkFrameTransformFromBeta(wg_system.betaVec());

    c_charged_lepton = boost.transform(lep);
    c_neutrino = boost.transform(neu);
    c_photon = boost.transform(pho);

    if (verbose) {
      cout << "> c_lepton   : " << c_charged_lepton << "\n";
      cout << "> c_neutrino : " << c_neutrino << "\n";
      cout << "> c_photon   : " << c_photon << "\n";
    }

    FourMomentum c_w_boson;
    c_w_boson += c_charged_lepton;
    c_w_boson += c_neutrino;

    Vector3 r_uvec = wg_system.vector3().unit();
    if (verbose) {
      cout << "> c_w_boson : " << c_w_boson << endl;
      cout << "> r_uvec   : " << r_uvec << endl;
    }

    Vector3 z_uvec = c_w_boson.vector3().unit();
    Vector3 y_uvec = z_uvec.cross(r_uvec).unit();
    Vector3 x_uvec = y_uvec.cross(z_uvec).unit();
    if (verbose) {
      cout << "> x_uvec   : " << x_uvec << endl;
      cout << "> y_uvec   : " << y_uvec << endl;
      cout << "> z_uvec   : " << z_uvec << endl;
    }

    Matrix3 rot_matrix;
    rot_matrix.setRow(0, x_uvec).setRow(1, y_uvec).setRow(2, z_uvec);
    auto rotator = LorentzTransform();
    rotator = rotator.postMult(rot_matrix);
    if (verbose) {
      cout << "> rotator   : " << rotator << endl;
    }
    r_w_boson = rotator.transform(c_w_boson);
    r_charged_lepton = rotator.transform(c_charged_lepton);
    r_neutrino = rotator.transform(c_neutrino);
    r_photon = rotator.transform(c_photon);

    if (verbose) {
      cout << "> r_lepton   : " << r_charged_lepton << endl;
      cout << "> r_neutrino : " << r_neutrino << endl;
      cout << "> r_photon   : " << r_photon << endl;
      cout << "> r_w_boson  : " << r_w_boson << endl;
    }
  }

  double CMS_2021_I1978840::WGSystem::phi() {
    double lep_phi = r_charged_lepton.phi(PhiMapping::MINUSPI_PLUSPI);
    return mapAngleMPiToPi(lepton_charge > 0 ? (lep_phi) : (lep_phi + PI));
  }

  double CMS_2021_I1978840::WGSystem::symphi() {
    double lep_phi = phi();
    if (lep_phi > PI / 2.) {
      return PI - lep_phi;
    } else if (lep_phi < -1. * (PI / 2.)) {
      return -1. * (PI + lep_phi);
    } else {
      return lep_phi;
    }
  }


  RIVET_DECLARE_PLUGIN(CMS_2021_I1978840);

}