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ZEUS_1999_I470499

Forward jet production in deep inelastic scattering at HERA (ZEUS)
Experiment: ZEUS (HERA)
Inspire ID: 470499
Status: VALIDATED
Authors:
  • Wendy Zhang
  • Hannes Jung
References: Beams: e+ p+, p+ e+
Beam energies: (27.5, 820.0); (820.0, 27.5) GeV
    No run details listed

The inclusive forward jet cross section in deep inelastic e+p scattering has been measured in the region of x-Bjorken, $4.5 \times 10^{-4}$ to $4.5 \times 10^{-2}$. This measurement is motivated by the search for effects of BFKL-like parton shower evolution. The cross section at hadron level as a function of x is compared to cross sections predicted by various Monte Carlo models. An excess of forward jet production at small x is observed, which is not reproduced by models based on DGLAP parton shower evolution.

Source code: ZEUS_1999_I470499.cc 
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/DISKinematics.hh"
#include "fastjet/SISConePlugin.hh"
#include<cmath>

namespace Rivet {


  /// @brief Forward jet production in deep inelastic scattering at HERA (ZEUS)
  class ZEUS_1999_I470499 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ZEUS_1999_I470499);


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

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

      // Initialise and register projections

      // The basic final-state projection:
      // all final-state particles within
      // the given eta acceptance
      const FinalState fs; /// SHOULD I KEEP THIS AT ALL?
      declare(fs, "FS");
        
      // declare jets
      double jet_radius = 1.0;///FIGURE THIS OUT
      declare(FastJets(fs, FastJets::PXCONE, jet_radius), "Jets");//FIGURE THE JET OUT
       
      // declare DIS Kinematics
      declare(DISLepton(), "Lepton");
      declare(DISKinematics(), "Kinematics");

      // take binning from reference data using HEPData ID (digits in "d01-x01-y01" etc.)
      book(_h["xbj"], 1, 1, 1);
  

    }


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

      // Retrieve dressed leptons, sorted by pT
      const FinalState& fs = apply<FinalState>(event, "FS");
        
      const size_t numParticles = fs.particles().size();

      if (numParticles < 2) {
          MSG_DEBUG("Failed leptonic event cut");
          vetoEvent;
        }
        
      const DISKinematics& dk = applyProjection<DISKinematics>(event, "Kinematics");
      const DISLepton& dl = applyProjection<DISLepton>(event,"Lepton");
        
      // Get the DIS kinematics
      double xbj  = dk.x();
      double ybj = dk.y();
      double Q2 = dk.Q2()/GeV;
      
      //cut on y
      if (ybj<0.1) vetoEvent;
      if (4.5*pow(10,-4)>xbj && xbj>4.5*pow(10,-2)) vetoEvent;
          

        
    //Frame transfer
      const LorentzTransform breitboost = dk.boostBreit();
    
        //on scattered lepton
        
          FourMomentum leptonMom = dl.out().momentum();
          double enel = leptonMom.E();
              
          bool cut = enel>10*GeV;
          if (!cut) vetoEvent;
        
        //scattered jets
       

        const Jets jets = apply<FastJets>(event, "Jets").jets(Cuts::Et > 5*GeV && Cuts::eta<2.6, cmpMomByEt);
        //Cuts::pz/(820*GeV)>0.036
        //&& Cuts::0.5<pow(Et,2)/Q2<2 && Cuts::breMom.pz>0
        
        bool loopjet=false;
        for (const Jet&j:jets){
            //cout << " j.pz "  << j.pz()/(820*GeV) << endl; 
            if (j.pz()/(820*GeV)<0.036) continue;
            // cout << pow(j.Et(),2) << endl;
            
            if (0.5>pow(j.Et(),2)/Q2||pow(j.Et(),2)/Q2>2) continue;
            FourMomentum breMom = breitboost.transform(j.momentum());
            //cout<< " pz " << breMom.pz() << endl; 
            if (breMom.pz()<0) continue;
            
            loopjet=true;
        }
        // cout<< " loojet " << loopjet << endl; 
        if(loopjet)  _h["xbj"]->fill(xbj);
        
        


      // Fill histogram with leading b-jet pT
        
    }


    /// Normalise histograms etc., after the run
    void finalize() {

      scale(_h["xbj"], crossSection()/nanobarn/sumW());
        //normalize(_h["xbj"]);

    }

    ///@}


    /// @name Histograms
    ///@{
    map<string, Histo1DPtr> _h;
    map<string, Profile1DPtr> _p;
    map<string, CounterPtr> _c;
    ///@}


  };


  RIVET_DECLARE_PLUGIN(ZEUS_1999_I470499);

}