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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 andrii.verbytskyi@mpp.mpg.de
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
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/FastJets.hh"
  5#include "Rivet/Projections/DISFinalState.hh"
  6#include "Rivet/Projections/DISKinematics.hh"
  7
  8namespace Rivet {
  9
 10
 11  /// @brief Multi-jet cross-sections in charged current $e^{\pm} p$ scattering at HERA
 12  class ZEUS_2008_I780108 : public Analysis {
 13  public:
 14
 15      /// Constructor
 16      RIVET_DEFAULT_ANALYSIS_CTOR(ZEUS_2008_I780108);
 17
 18      /// @name Analysis methods
 19      /// @{
 20
 21      /// Book histograms and initialise projections before the run
 22      void init() {
 23
 24          // Projections
 25          const DISKinematics diskin;
 26          declare(diskin, "Kinematics");
 27          const DISFinalState disfs(DISFinalState::BoostFrame::LAB);
 28          FastJets jets(disfs, FastJets::KT, 1.0);
 29          declare(jets, "Jets");
 30
 31          // Table 11
 32          book(_h_eta_incl[0], 11, 1, 1);
 33          book(_h_eta_incl[1], 11, 1, 2);
 34          // Table 12
 35          book(_h_eta_di[0], 12, 1, 1);
 36          book(_h_eta_di[1], 12, 1, 2);
 37          // Table 13
 38          book(_h_eta_tri[0], 13, 1, 1);
 39          book(_h_eta_tri[1], 13, 1, 2);
 40          // Table 14
 41          book(_h_et_incl[0], 14, 1, 1);
 42          book(_h_et_incl[1], 14, 1, 2);
 43          // Table 15
 44          book(_h_et_di[0], 15, 1, 1);
 45          book(_h_et_di[1], 15, 1, 2);
 46          // Table 16
 47          book(_h_et_tri[0], 16, 1, 1);
 48          book(_h_et_tri[1], 16, 1, 2);
 49          // Table 17
 50          book(_h_q2_incl[0], 17, 1, 1);
 51          book(_h_q2_incl[1], 17, 1, 2);
 52          // Table 18
 53          book(_h_q2_di[0], 18, 1, 1);
 54          book(_h_q2_di[1], 18, 1, 2);
 55          // Table 19
 56          book(_h_q2_tri[0], 19, 1, 1);
 57          book(_h_q2_tri[1], 19, 1, 2);
 58
 59          // Table 20
 60          book(_h_x_incl[0], 20, 1, 1);
 61          book(_h_x_incl[1], 20, 1, 2);
 62          // Table 22
 63          book(_h_m_di[0], 22, 1, 1);
 64          book(_h_m_di[1], 22, 1, 2);
 65          // Table 23
 66          book(_h_m_tri[0], 23, 1, 1);
 67          book(_h_m_tri[1], 23, 1, 2);
 68
 69      }
 70
 71
 72      /// Perform the per-event analysis
 73      void analyze(const Event& event) {
 74
 75          int fLepton = 0;
 76
 77          const ParticlePair bs = event.beams();
 78          if (bs.first.pid() == PID::POSITRON || bs.second.pid() == PID::POSITRON) fLepton = 1;
 79          const Particle& bproton = (bs.first.pid() == PID::PROTON) ? bs.first : bs.second;
 80          const int orientation = sign(bproton.momentum().pz());
 81          // DIS kinematics
 82          const DISKinematics& dk = apply<DISKinematics>(event, "Kinematics");
 83          double q2  = dk.Q2();
 84          double x   = dk.x();
 85          double y   = dk.y();
 86
 87          if (q2 < 200) vetoEvent;
 88          if (y > 0.9) vetoEvent;
 89          // Jet selection
 90          const Jets jets = apply<FastJets>(event, "Jets").jets(Cuts::Et > 5*GeV && Cuts::etaIn(-1*orientation, 2.5*orientation), cmpMomByEt);
 91          MSG_DEBUG("Jet multiplicity = " << jets.size());
 92          if (jets.size() < 1) vetoEvent;
 93          if (jets[0].Et() < 14*GeV) vetoEvent;
 94
 95          double eta12 = 0;
 96          double et12 = 0;
 97
 98          double et123 = 0;
 99          double eta123 =0;
100
101          for (size_t i = 0; i < jets.size(); i++)
102          {
103              if (jets[i].Et() < 14*GeV) continue;
104              _h_eta_incl[fLepton]->fill(orientation*jets[i].eta());
105              _h_et_incl[fLepton]->fill(jets[i].Et());
106              _h_q2_incl[fLepton]->fill(q2);
107              _h_x_incl[fLepton]->fill(x);
108          }
109
110          if (jets.size() > 1)
111          {
112              eta12 = orientation*(jets[0].eta() + jets[1].eta())/2;
113              et12 = (jets[0].Et() + jets[1].Et())/2;
114              _h_eta_di[fLepton]->fill(eta12);
115              _h_et_di[fLepton]->fill(et12);
116              _h_q2_di[fLepton]->fill(q2);
117              _h_m_di[fLepton]->fill(   (jets[0].momentum()+jets[1].momentum()).mass());
118          }
119
120          if (jets.size() > 2)
121          {
122              eta123 = orientation*(jets[0].eta() + jets[1].eta()+jets[2].eta())/3;
123              et123 = (jets[0].Et() + jets[1].Et()+jets[2].Et())/3;
124
125              _h_eta_tri[fLepton]->fill(eta123);
126              _h_et_tri[fLepton]->fill(et123);
127              _h_q2_tri[fLepton]->fill(q2);
128              _h_m_tri[fLepton]->fill(   (jets[0].momentum()+jets[1].momentum()+jets[2].momentum()).mass());
129          }
130      }
131
132
133      /// Normalise histograms etc., after the run
134      void finalize() {
135          const double sf = crossSection()/picobarn/sumOfWeights();
136
137
138          scale(_h_eta_incl, sf);
139          scale(_h_eta_di,   sf);
140          scale(_h_eta_tri,  sf);
141          scale(_h_et_incl,  sf);
142          scale(_h_et_di,    sf);
143          scale(_h_et_tri,   sf);
144          scale(_h_q2_incl,  sf);
145          scale(_h_q2_di,    sf);
146          scale(_h_q2_tri,   sf);
147          scale(_h_x_incl,   sf);
148          scale(_h_m_di,     sf);
149          scale(_h_m_tri,    sf);
150
151      }
152
153      /// @}
154
155
156      /// @name Histograms
157      /// @{
158      Histo1DPtr _h_eta_incl[2], _h_eta_di[2], _h_eta_tri[2];
159      Histo1DPtr _h_et_incl[2], _h_et_di[2], _h_et_tri[2];
160      Histo1DPtr _h_q2_incl[2], _h_q2_di[2], _h_q2_tri[2];
161      Histo1DPtr _h_x_incl[2], _h_x_di[2], _h_x_tri[2];
162      Histo1DPtr _h_m_di[2], _h_m_tri[2];
163      /// @}
164  };
165
166
167  RIVET_DECLARE_PLUGIN(ZEUS_2008_I780108);
168
169}