Rivet analyses

title: ZEUS_2008_I780108

Multi-jet cross-sections in charged current $e^{\pm} p$ scattering at HERA

Experiment: ZEUS (HERA)

Inspire ID: 780108

Status: VALIDATED

Authors: - Andrii Verbytskyi

References: - arXiv: 0802.3955 - Phys. Rev. D78 (2008) 032004

Beams: p+ e-, p+ e+, e- p+, e+ p+

Beam energies: ANY

Run details: - inclusive ep collisons

Jet cross sections were measured in charged current deep inelastic $e^{\pm}p$ scattering at high boson virtualities $Q^2$ with the ZEUS detector at HERA II using an integrated luminosity of $0.36 fb^{-1}$. Differential cross sections are presented for inclusive-jet production as functions of $Q^2$, Bjorken x and the jet transverse energy and pseudorapidity. The dijet invariant mass cross section is also presented. Observation of three- and four-jet events in charged-current $e^{\pm}p$ processes is reported for the first time. The predictions of next-to-leading-order (NLO) QCD calculations are compared to the measurements. The measured inclusive-jet cross sections are well described in shape and normalization by the NLO predictions. The data have the potential to constrain the u and d valence quark distributions in the proton if included as input to global fits.

Source code:ZEUS_2008_I780108.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DISFinalState.hh"

include "Rivet/Projections/DISKinematics.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief Multi-jet cross-sections in charged current $e^{\pm} p$ scattering at HERA class ZEUS_2008_I780108 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ZEUS_2008_I780108);

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

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

  // Projections
  const DISKinematics diskin;
  declare(diskin, "Kinematics");
  declare(DISLepton(), "Lepton");
  const DISFinalState disfs(DISFrame::LAB);
  FastJets jets(disfs, JetAlg::KT, 1.0);
  declare(jets, "Jets");

  // Table 11
  book(_h_eta_incl[0], 11, 1, 1);
  book(_h_eta_incl[1], 11, 1, 2);
  // Table 12
  book(_h_eta_di[0], 12, 1, 1);
  book(_h_eta_di[1], 12, 1, 2);
  // Table 13
  book(_h_eta_tri[0], 13, 1, 1);
  book(_h_eta_tri[1], 13, 1, 2);
  // Table 14
  book(_h_et_incl[0], 14, 1, 1);
  book(_h_et_incl[1], 14, 1, 2);
  // Table 15
  book(_h_et_di[0], 15, 1, 1);
  book(_h_et_di[1], 15, 1, 2);
  // Table 16
  book(_h_et_tri[0], 16, 1, 1);
  book(_h_et_tri[1], 16, 1, 2);
  // Table 17
  book(_h_q2_incl[0], 17, 1, 1);
  book(_h_q2_incl[1], 17, 1, 2);
  // Table 18
  book(_h_q2_di[0], 18, 1, 1);
  book(_h_q2_di[1], 18, 1, 2);
  // Table 19
  book(_h_q2_tri[0], 19, 1, 1);
  book(_h_q2_tri[1], 19, 1, 2);

  // Table 20
  book(_h_x_incl[0], 20, 1, 1);
  book(_h_x_incl[1], 20, 1, 2);
  // Table 22
  book(_h_m_di[0], 22, 1, 1);
  book(_h_m_di[1], 22, 1, 2);
  // Table 23
  book(_h_m_tri[0], 23, 1, 1);
  book(_h_m_tri[1], 23, 1, 2);
}


/// Perform the per-event analysis
void analyze(const Event& event) {

  int fLepton = 0;

  const ParticlePair bs = event.beams();
  if (bs.first.pid() == PID::POSITRON || bs.second.pid() == PID::POSITRON) fLepton = 1;
  const Particle& bproton = (bs.first.pid() == PID::PROTON) ? bs.first : bs.second;
  const int orientation = sign(bproton.momentum().pz());
  // DIS kinematics
  const DISKinematics& dk = apply<DISKinematics>(event, "Kinematics");
  double q2 = dk.Q2();
  double x = dk.x();
  double y = dk.y();

  if (q2 < 200) vetoEvent;
  if (y > 0.9) vetoEvent;
  // make sure charged current
  const DISLepton& dl = apply<DISLepton>(event, "Lepton");
  if (!PID::isNeutrino(dl.out().abspid())) vetoEvent;
  // Jet selection
  const Jets jets = apply<FastJets>(event, "Jets")
                        .jets(Cuts::Et > 5 * GeV && Cuts::etaIn(-1 * orientation, 2.5 * orientation),
                              cmpMomByEt);
  MSG_DEBUG("Jet multiplicity = " << jets.size());
  if (jets.size() < 1) vetoEvent;
  if (jets[0].Et() < 14 * GeV) vetoEvent;

  double eta12 = 0;
  double et12 = 0;

  double et123 = 0;
  double eta123 = 0;

  for (size_t i = 0; i < jets.size(); ++i) {
    if (jets[i].Et() < 14 * GeV) continue;
    _h_eta_incl[fLepton]->fill(orientation * jets[i].eta());
    _h_et_incl[fLepton]->fill(jets[i].Et());
    _h_q2_incl[fLepton]->fill(q2);
    _h_x_incl[fLepton]->fill(x);
  }

  if (jets.size() > 1) {
    eta12 = orientation * (jets[0].eta() + jets[1].eta()) / 2;
    et12 = (jets[0].Et() + jets[1].Et()) / 2;
    _h_eta_di[fLepton]->fill(eta12);
    _h_et_di[fLepton]->fill(et12);
    _h_q2_di[fLepton]->fill(q2);
    _h_m_di[fLepton]->fill((jets[0].momentum() + jets[1].momentum()).mass());
  }

  if (jets.size() > 2) {
    eta123 = orientation * (jets[0].eta() + jets[1].eta() + jets[2].eta()) / 3;
    et123 = (jets[0].Et() + jets[1].Et() + jets[2].Et()) / 3;

    _h_eta_tri[fLepton]->fill(eta123);
    _h_et_tri[fLepton]->fill(et123);
    _h_q2_tri[fLepton]->fill(q2);
    _h_m_tri[fLepton]->fill((jets[0].momentum() + jets[1].momentum() + jets[2].momentum()).mass());
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  const double sf = crossSection() / picobarn / sumOfWeights();


  scale(_h_eta_incl, sf);
  scale(_h_eta_di, sf);
  scale(_h_eta_tri, sf);
  scale(_h_et_incl, sf);
  scale(_h_et_di, sf);
  scale(_h_et_tri, sf);
  scale(_h_q2_incl, sf);
  scale(_h_q2_di, sf);
  scale(_h_q2_tri, sf);
  scale(_h_x_incl, sf);
  scale(_h_m_di, sf);
  scale(_h_m_tri, sf);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_eta_incl[2], _h_eta_di[2], _h_eta_tri[2];
Histo1DPtr _h_et_incl[2], _h_et_di[2], _h_et_tri[2];
Histo1DPtr _h_q2_incl[2], _h_q2_di[2], _h_q2_tri[2];
Histo1DPtr _h_x_incl[2], _h_x_di[2], _h_x_tri[2];
Histo1DPtr _h_m_di[2], _h_m_tri[2];
/// @}

};

RIVET_DECLARE_PLUGIN(ZEUS_2008_I780108);

} ```