Rivet analyses

title: MC_DILEPTON

Charged dilepton kinematic distributions sensitive to boson polarisation

Experiment: ()

Status: VALIDATED

Authors: - Andy Buckley

References: none listed

Beams: * *

Beam energies: ANY

Run details: - Any event type that produces prompt charged lepton pairs.

Finds two charged leptons ($e$ or $\mu$) and plots their basic kinematics in the lab frame and in their centre-of-mass frame. Observables of the lepton momentum components parallel and perpendicular to the CoM boost direction are particularly sensitive to the polarisation state of a decaying vector boson.

Source code:MC_DILEPTON.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/PromptFinalState.hh"

namespace Rivet {

/// @brief Study of prompt dilepton kinematics sensitive to boson polarizations class MC_DILEPTON : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(MC_DILEPTON);


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

/// Book histograms and initialise projections before the run
void init() {

  // set FS cuts from input options
  const double etacut = getOption<double>("ABSETALMAX", 5.);
  const double ptcut = getOption<double>("PTLMIN", 10.);

  // Initialise and register projections
  declare(PromptFinalState((Cuts::abspid == PID::ELECTRON || Cuts::abspid == PID::MUON)
                           && Cuts::abseta < etacut && Cuts::pT > ptcut * GeV),
          "Leptons");

  // Book histograms
  book(_h_pt_l1, "lep1_pt", logspace(40, 10, 400));
  book(_h_costheta_l1, "lep1_costheta", linspace(25, -1, 1));
  book(_h_ppara_l1, "lep1_ppara", linspace(40, -50, 350));
  book(_h_pperp_l1, "lep1_pperp", linspace(25, 0, 100));
  //
  book(_h_pt_l2, "lep2_pt", logspace(40, 10, 400));
  book(_h_costheta_l2, "lep2_costheta", linspace(25, -1, 1));
  book(_h_ppara_l2, "lep2_ppara", linspace(40, -50, 350));
  book(_h_pperp_l2, "lep2_pperp", linspace(25, 0, 100));
  //
  book(_h_costheta_com_l1, "com_costheta_l1", linspace(25, -1, 1));
  book(_h_costheta_com_l2, "com_costheta_l2", linspace(25, -1, 1));
  book(_h_ppara_com_l1, "com_ppara_l1", linspace(25, -50, 50));
  book(_h_ppara_com_l2, "com_ppara_l2", linspace(25, -50, 50));
  //
  book(_h_costheta_com, "com_costheta", linspace(25, -1, 1));
  book(_h_ppara_com, "com_ppara", linspace(25, -50, 50));
  book(_h_pperp_com, "com_pperp", linspace(25, 0, 100));
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const Particles& leptons = apply<FinalState>(event, "Leptons").particlesByPt();
  if (leptons.size() != 2) vetoEvent;
  const Particle& l1 = leptons[0];
  const Particle& l2 = leptons[1];
  _h_pt_l1->fill(l1.pT() / GeV);
  _h_pt_l2->fill(l2.pT() / GeV);

  const FourMomentum pcom = l1.mom() + l2.mom();
  const Vector3 betacom = pcom.betaVec();
  const Vector3 unitboostvec = betacom.unit();
  const LorentzTransform comboost = LorentzTransform::mkFrameTransformFromBeta(betacom);

  const double l1_costheta = cos(l1.p3().angle(unitboostvec));
  const double l1_ppara = l2.p3().dot(unitboostvec);
  const double l1_pperp = l2.p3().cross(unitboostvec).mod();
  _h_costheta_l1->fill(l1_costheta);
  _h_ppara_l1->fill(l1_ppara);
  _h_pperp_l1->fill(l1_pperp);

  const double l2_costheta = cos(l2.p3().angle(unitboostvec));
  const double l2_ppara = l2.p3().dot(unitboostvec);
  const double l2_pperp = l2.p3().cross(unitboostvec).mod();
  _h_costheta_l2->fill(l2_costheta);
  _h_ppara_l2->fill(l2_ppara);
  _h_pperp_l2->fill(l2_pperp);

  const FourMomentum p1com = comboost.transform(l1.mom());
  const FourMomentum p2com = comboost.transform(l2.mom());
  const double com_costheta1 = cos(p1com.p3().angle(unitboostvec));
  const double com_costheta2 = cos(p2com.p3().angle(unitboostvec));
  MSG_DEBUG("CoM cos(th)s: " << com_costheta1 << ", " << com_costheta2);
  // assert(com_costheta1 == com_costheta2 && "CoM cos(th)s differ");
  const double com_ppara1 = p1com.p3().dot(unitboostvec);
  const double com_ppara2 = p2com.p3().dot(unitboostvec);
  MSG_DEBUG("CoM p_paras: " << com_ppara1 << ", " << com_ppara2);
  // assert(com_ppara1 == com_ppara2 && "CoM p_paras differ");
  const double com_pperp1 = p1com.p3().cross(unitboostvec).mod();
  const double com_pperp2 = p2com.p3().cross(unitboostvec).mod();
  MSG_DEBUG("CoM p_pperps: " << com_pperp1 << ", " << com_pperp2);
  // assert(com_pperp1 == com_pperp2 && "CoM p_perps differ");
  _h_costheta_com_l1->fill(com_costheta1);
  _h_costheta_com_l2->fill(com_costheta2);
  _h_costheta_com->fill(com_costheta1, 0.5);
  _h_costheta_com->fill(com_costheta2, 0.5);
  _h_ppara_com_l1->fill(com_ppara1);
  _h_ppara_com_l2->fill(com_ppara2);
  _h_ppara_com->fill(com_ppara1, 0.5);
  _h_ppara_com->fill(com_ppara2, 0.5);
  _h_pperp_com->fill(com_pperp1);
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_pt_l1);
  normalize(_h_pt_l2);
  normalize(_h_ppara_com);
  normalize(_h_pperp_com);
  normalize(_h_costheta_com);
  normalize(_h_ppara_com_l1);
  normalize(_h_ppara_com_l2);
  normalize(_h_costheta_com_l1);
  normalize(_h_costheta_com_l2);
  normalize(_h_ppara_l1);
  normalize(_h_pperp_l1);
  normalize(_h_costheta_l1);
  normalize(_h_ppara_l2);
  normalize(_h_pperp_l2);
  normalize(_h_costheta_l2);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_pt_l1, _h_pt_l2;
Histo1DPtr _h_ppara_com, _h_pperp_com, _h_costheta_com;
Histo1DPtr _h_ppara_com_l1, _h_ppara_com_l2, _h_costheta_com_l1, _h_costheta_com_l2;
Histo1DPtr _h_ppara_l1, _h_pperp_l1, _h_costheta_l1;
Histo1DPtr _h_ppara_l2, _h_pperp_l2, _h_costheta_l2;
/// @}

};

RIVET_DECLARE_PLUGIN(MC_DILEPTON);

} ```