Rivet analyses

title: H1_2006_I711847

Dijet photoproduction analysis

Experiment: H1 (HERA Run II)

Inspire ID: 711847

Status: UNVALIDATED

Authors: - Ilkka Helenius

References: - Phys.Lett. B639 (2006) 21-31 - DESY 06/020 - arXiv: hep-ex/0603014

Beams: p+ e+

Beam energies: (920.0, 27.6)GeV

Run details: - 920 GeV protons colliding with 27.6 GeV positrons; Direct and resolved photoproduction of dijets; Jet pseudorapidity $-0.5 < |\eta| < 2.75$ Leading jet $ET > 25$ GeV, second jet $pT > 15$ GeV; Virtuality $Q^2 < 1.0$ GeV;

H1 photoproduction of of jets from proton--positron collisions at beam energies of 920~GeV on 27.5~GeV. Total integrated luminosity 66.6 pb$^-1$.

Source code:H1_2006_I711847.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/DISFinalState.hh"

include "Rivet/Projections/DISKinematics.hh"

include "Rivet/Projections/FastJets.hh"

namespace Rivet {

/// @brief H1 dijet photoproduction /// /// @note Cleaning cuts on event pT/sqrt(Et) and y_e are not needed in MC analysis. class H1_2006_I711847 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(H1_2006_I711847);

/// @name Analysis methods
//@{

// Book projections and histograms
void init() {

  /// @todo Acceptance
  const FinalState& fs = declare(DISFinalState(DISFrame::LAB), "FS");
  declare(FastJets(fs, JetAlg::KT, 1.0), "Jets");

  // Projections
  declare(DISKinematics(), "Kinematics");

  // Table 1
  book(_h_costh[0], 1, 1, 1);
  book(_h_costh[1], 1, 1, 2);
  // Table 2
  book(_h_costh_mjj[0], 2, 1, 1);
  book(_h_costh_mjj[1], 2, 1, 2);
  // Table 3
  book(_h_xgamma[0], 3, 1, 1);
  book(_h_xgamma[1], 3, 1, 2);
  // Table 4
  book(_h_xproton[0], 4, 1, 1);
  book(_h_xproton[1], 5, 1, 1);
  book(_h_xproton[2], 6, 1, 1);
  book(_h_xproton[3], 7, 1, 1);
  book(_h_xproton[4], 8, 1, 1);
  book(_h_xproton[5], 9, 1, 1);
  // Table 5
  book(_h_etjet1[0], 10, 1, 1);
  book(_h_etjet1[1], 11, 1, 1);
  book(_h_etjet1[2], 12, 1, 1);
  book(_h_etjet1[3], 13, 1, 1);
  book(_h_etjet1[4], 14, 1, 1);
  book(_h_etjet1[5], 15, 1, 1);
}

// Do the analysis
void analyze(const Event& event) {

  // Determine event orientation, since coord system is for +z = proton direction
  const ParticlePair bs = event.beams();
  if (bs.first.pid() != PID::POSITRON && bs.second.pid() != PID::POSITRON) vetoEvent;
  const Particle& bpositron = (bs.first.pid() == PID::POSITRON ? bs.first : bs.second);
  if (bs.first.pid() != PID::PROTON && bs.second.pid() != PID::PROTON) vetoEvent;
  const Particle& bproton = (bs.first.pid() == PID::PROTON) ? bs.first : bs.second;
  const int orientation = sign(bproton.momentum().pz());
  MSG_DEBUG("Beam proton = " << bproton.mom() << " GeV => orientation = " << orientation);

  // Jet selection
  const Jets jets = apply<FastJets>(event, "Jets")
                        .jets(Cuts::Et > 15 * GeV && Cuts::etaIn(-0.5 * orientation, 2.75 * orientation),
                              cmpMomByEt);
  MSG_DEBUG("Jet multiplicity = " << jets.size());
  if (jets.size() < 2) vetoEvent;
  const Jet& j1 = jets[0];
  const Jet& j2 = jets[1];
  if (j1.Et() < 25 * GeV) vetoEvent;

  // eta and cos(theta*) computation
  const double eta1 = orientation * j1.eta(), eta2 = orientation * j2.eta();
  const double etadiff = eta1 - eta2;
  const double costhetastar = tanh(0.5 * etadiff);

  // DIS kinematics
  const DISKinematics& dk = apply<DISKinematics>(event, "Kinematics");
  double q2 = dk.Q2();
  double y = dk.y();

  if (q2 > 1.) vetoEvent;

  // Computation and cut on inelasticity
  if (!inRange(y, 0.1, 0.9)) vetoEvent;

  // Computation of x_y^obs
  const double xphoton = (j1.Et() * exp(-eta1) + j2.Et() * exp(-eta2)) / (2 * y * bpositron.E());
  const double xproton = (j1.Et() * exp(eta1) + j2.Et() * exp(eta2)) / (2 * bproton.E());

  const size_t i_xphoton = (xphoton < 0.8) ? 0 : 1;
  const size_t i_xproton = (xproton < 0.1) ? 0 : 1;

  // Calculate the invariant mass of the dijet as in the paper
  const double mjj = sqrt(2. * j1.Et() * j2.Et()
                          * (cosh(j1.eta() - j2.eta()) - cos(j1.phi() - j2.phi())));

  // Fill histograms
  // T1
  _h_costh[i_xphoton]->fill(abs(costhetastar));
  // T2
  if (mjj > 65 * GeV) _h_costh_mjj[i_xphoton]->fill(abs(costhetastar));
  // T3
  _h_xgamma[i_xproton]->fill(xphoton);

  // T4
  if (eta1 < 1 && eta2 < 1) _h_xproton[3 * i_xphoton]->fill(xproton);
  if (eta1 > 1 && eta2 < 1) _h_xproton[1 + 3 * i_xphoton]->fill(xproton);
  if (eta2 > 1 && eta1 < 1) _h_xproton[1 + 3 * i_xphoton]->fill(xproton);
  if (eta1 > 1 && eta2 > 1) _h_xproton[2 + 3 * i_xphoton]->fill(xproton);
  // T5
  if (eta1 < 1 && eta2 < 1) _h_etjet1[3 * i_xphoton]->fill(j1.Et() / GeV);
  if (eta1 > 1 && eta2 < 1) _h_etjet1[1 + 3 * i_xphoton]->fill(j1.Et() / GeV);
  if (eta2 > 1 && eta1 < 1) _h_etjet1[1 + 3 * i_xphoton]->fill(j1.Et() / GeV);
  if (eta1 > 1 && eta2 > 1) _h_etjet1[2 + 3 * i_xphoton]->fill(j1.Et() / GeV);
  // }
}

// Finalize
void finalize() {
  const double sf = crossSection() / picobarn / sumOfWeights();
  scale(_h_costh, sf);
  scale(_h_costh_mjj, sf);
  scale(_h_xgamma, sf);
  scale(_h_xproton, sf);
  scale(_h_etjet1, sf);
}

//@}

private:

/// @name Histograms
//@{
Histo1DPtr _h_costh[2], _h_costh_mjj[2], _h_xgamma[2], _h_xproton[6], _h_etjet1[6];
//@}

};

RIVET_DECLARE_PLUGIN(H1_2006_I711847);

} ```