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Rivet analyses reference

H1_1994_S2919893

H1 energy flow and charged particle spectra in DIS
Experiment: H1 (HERA)
Inspire ID: 372350
Status: VALIDATED
Authors:
  • Peter Richardson
References: Beams: p+ e-, p+ e+
Beam energies: (820.0, 26.7) GeV
Run details:
  • $e^- p$ / $e^+ p$ deep inelastic scattering, 820 GeV protons colliding with 26.7 GeV electrons

Global properties of the hadronic final state in deep inelastic scattering events at HERA are investigated. The data are corrected for detector effects. Energy flows in both the laboratory frame and the hadronic centre of mass system, and energy-energy correlations in the laboratory frame are presented. Historically, the Ariadne colour dipole model provided the only satisfactory description of this data, hence making it a useful 'target' analysis for MC shower models.

Source code: H1_1994_S2919893.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Math/Constants.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/DISKinematics.hh"

namespace Rivet {


  /// @brief H1 energy flow and charged particle spectra
  /// @author Peter Richardson
  /// Based on the equivalent HZTool analysis
  class H1_1994_S2919893 : public Analysis {
  public:

    /// Constructor
    H1_1994_S2919893()
      : Analysis("H1_1994_S2919893")
    {

      // Initialise member variables
      _w77  = make_pair(0.0, 0.0);
      _w122 = make_pair(0.0, 0.0);
      _w169 = make_pair(0.0, 0.0);
      _w117 = make_pair(0.0, 0.0);
      _wEnergy = make_pair(0.0, 0.0);
    }


    /// @name Analysis methods
    //@{

    /// Initialise projections and histograms
    void init() {
      // Projections
      declare(DISLepton(), "Lepton");
      declare(DISKinematics(), "Kinematics");
      declare(FinalState(), "FS");

      // Histos
      _histEnergyFlowLowX =  bookHisto1D(1, 1, 1);
      _histEnergyFlowHighX = bookHisto1D(1, 1, 2);

      _histEECLowX = bookHisto1D(2, 1, 1);
      _histEECHighX = bookHisto1D(2, 1, 2);

      _histSpectraW77 = bookHisto1D(3, 1, 1);
      _histSpectraW122 = bookHisto1D(3, 1, 2);
      _histSpectraW169 = bookHisto1D(3, 1, 3);
      _histSpectraW117 = bookHisto1D(3, 1, 4);

      _histPT2 = bookProfile1D(4, 1, 1);
    }


    /// Analyse each event
    void analyze(const Event& event) {

      // Get the DIS kinematics
      const DISKinematics& dk = apply<DISKinematics>(event, "Kinematics");
      const double x  = dk.x();
      const double w2 = dk.W2();
      const double w = sqrt(w2);

      // Momentum of the scattered lepton
      const DISLepton& dl = apply<DISLepton>(event,"Lepton");
      const FourMomentum leptonMom = dl.out();
      const double ptel = leptonMom.pT();
      const double enel = leptonMom.E();
      const double thel = leptonMom.angle(dk.beamHadron().mom())/degree;

      // Extract the particles other than the lepton
      const FinalState& fs = apply<FinalState>(event, "FS");
      Particles particles;
      particles.reserve(fs.particles().size());
      const GenParticle* dislepGP = dl.out().genParticle();
      foreach (const Particle& p, fs.particles()) {
        const GenParticle* loopGP = p.genParticle();
        if (loopGP == dislepGP) continue;
        particles.push_back(p);
      }

      // Cut on the forward energy
      double efwd = 0.0;
      foreach (const Particle& p, particles) {
        const double th = p.angle(dk.beamHadron())/degree;
        if (inRange(th, 4.4, 15)) efwd += p.E();
      }

      // Apply the cuts
      // Lepton energy and angle, w2 and forward energy
      MSG_DEBUG("enel/GeV = " << enel/GeV << ", thel = " << thel
                << ", w2 = " << w2 << ", efwd/GeV = " << efwd/GeV);
      bool cut = enel/GeV > 14. && thel > 157. && thel < 172.5 && w2 >= 3000. && efwd/GeV > 0.5;
      if (!cut) vetoEvent;

      // Weight of the event
      const double weight = event.weight();
      (x < 1e-3 ? _wEnergy.first : _wEnergy.second) += weight;

      // Boost to hadronic CM
      const LorentzTransform hcmboost = dk.boostHCM();
      // Loop over the particles
      long ncharged(0);
      for (size_t ip1 = 0; ip1 < particles.size(); ++ip1) {
        const Particle& p = particles[ip1];

        const double th = p.angle(dk.beamHadron().momentum()) / degree;
        // Boost momentum to lab
        const FourMomentum hcmMom = hcmboost.transform(p.momentum());
        // Angular cut
        if (th <= 4.4) continue;

        // Energy flow histogram
        const double et = fabs(hcmMom.Et());
        const double eta = hcmMom.eta();
        (x < 1e-3 ? _histEnergyFlowLowX : _histEnergyFlowHighX)->fill(eta, et*weight);
        if (PID::threeCharge(p.pid()) != 0) {
          /// @todo Use units in w comparisons... what are the units?
          if (w > 50. && w <= 200.) {
            double xf= 2 * hcmMom.z() / w;
            double pt2 = hcmMom.pT2();
            if (w > 50. && w <= 100.) {
              _histSpectraW77 ->fill(xf, weight);
            } else if (w > 100. && w <= 150.) {
              _histSpectraW122->fill(xf, weight);
            } else if (w > 150. && w <= 200.) {
              _histSpectraW169->fill(xf, weight);
            }
            _histSpectraW117->fill(xf, weight);
            /// @todo Is this profile meant to be filled with 2 weight factors?
            _histPT2->fill(xf, pt2*weight/GeV2, weight);
            ++ncharged;
          }
        }


        // Energy-energy correlation
        if (th <= 8.) continue;
        double phi1 = p.phi(ZERO_2PI);
        double eta1 = p.eta();
        double et1 = fabs(p.momentum().Et());
        for (size_t ip2 = ip1+1; ip2 < particles.size(); ++ip2) {
          const Particle& p2 = particles[ip2];

          //double th2 = beamAngle(p2.momentum(), order);
          double th2 = p2.angle(dk.beamHadron().momentum()) / degree;
          if (th2 <= 8.) continue;
          double phi2 = p2.phi(ZERO_2PI);

          /// @todo Use angle function
          double deltaphi = phi1 - phi2;
          if (fabs(deltaphi) > PI) deltaphi = fabs(fabs(deltaphi) - TWOPI);
          double eta2 = p2.eta();
          double omega = sqrt(sqr(eta1-eta2) + sqr(deltaphi));
          double et2 = fabs(p2.momentum().Et());
          double wt = et1*et2 / sqr(ptel) * weight;
          (x < 1e-3 ? _histEECLowX : _histEECHighX)->fill(omega, wt);
        }
      }

      // Factors for normalization
      if (w > 50. && w <= 200.) {
        if (w <= 100.) {
          _w77.first  += ncharged*weight;
          _w77.second += weight;
        } else if (w <= 150.) {
          _w122.first  += ncharged*weight;
          _w122.second += weight;
        } else {
          _w169.first  += ncharged*weight;
          _w169.second += weight;
        }
        _w117.first  += ncharged*weight;
        _w117.second += weight;
      }
    }


    // Normalize inclusive single particle distributions to the average number of charged particles per event.
    void finalize() {
      normalize(_histSpectraW77, _w77.first/_w77.second);
      normalize(_histSpectraW122, _w122.first/_w122.second);
      normalize(_histSpectraW169, _w169.first/_w169.second);
      normalize(_histSpectraW117, _w117.first/_w117.second);

      scale(_histEnergyFlowLowX , 1./_wEnergy.first );
      scale(_histEnergyFlowHighX, 1./_wEnergy.second);

      scale(_histEECLowX , 1./_wEnergy.first );
      scale(_histEECHighX, 1./_wEnergy.second);
    }

    //@}


  private:

    /// Polar angle with right direction of the beam
    inline double beamAngle(const FourVector& v, bool order) {
      double thel = v.polarAngle()/degree;
      if (thel < 0) thel += 180.;
      if (!order) thel = 180 - thel;
      return thel;
    }

    /// @name Histograms
    //@{
    Histo1DPtr _histEnergyFlowLowX, _histEnergyFlowHighX;
    Histo1DPtr _histEECLowX, _histEECHighX;
    Histo1DPtr _histSpectraW77, _histSpectraW122, _histSpectraW169, _histSpectraW117;
    Profile1DPtr _histPT2;
    //@}

    /// @name Storage of weights to calculate averages for normalisation
    //@{
    pair<double,double> _w77, _w122, _w169, _w117, _wEnergy;
    //@}

  };



  DECLARE_RIVET_PLUGIN(H1_1994_S2919893);

}