Rivet analyses

title: H1_2002_I581409

Dijet cross-sections in photoproduction

Experiment: H1 (HERA)

Inspire ID: 581409

Status: VALIDATED

Authors: - Vithyaban Anjelo Narendra

References: - Eur.Phys.J.C 25 (2002) 13-23 - arXiv: hep-ex/0201006

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

Beam energies: (820.0, 27.6); (27.6, 820.0); (820.0, 27.6); (27.6, 820.0)GeV

Run details: - Photoproduction in HERA I

Dijet cross sections as functions of several jet observables are measured in photoproduction using the H1 detector at HERA. The data sample comprises $e^+p$ data with an integrated luminosity of 34.9 pb$^{-1}$. Jets are selected using the inclusive $k_\perp$ algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction $x_p$ and photon longitudinal momentum fraction $x_\gamma$ in the ranges $0.05 < x_p < 0.6$ and $0.1 < x_\gamma < 1$. The predictions of next-to-leading order perturbative QCD, including recent photon and proton parton densities, are found to be compatible with the data in a wide kinematical range.

Source code:H1_2002_I581409.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DISFinalState.hh"

include "Rivet/Projections/FastJets.hh"

namespace Rivet {

/// @brief Dijet cross-sections in photoproduction class H1_2002_I581409 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(H1_2002_I581409);


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

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

  // DIS final state
  const DISFinalState dfs(DISFrame::LAB);
  declare(dfs, "dfs");

  declare(FastJets(dfs, JetAlg::KT, 1.0), "jets");

  // Book histograms
  // Table1, T2, F2
  book(_h["mjj"], 1, 1, 1);

  // Table2, T2, F2A
  book(_h["Et_mean"], 2, 1, 1);

  // Table3, T2, F2B
  book(_h["Et_max"], 3, 1, 1);

  // Table4 , T3 F3AB
  book(_h["eta_bar_A"], 4, 1, 1);
  book(_h["eta_bar_B"], 4, 1, 2);

  // Table5, T3, F3CD
  book(_h["eta_bar_C"], 5, 1, 1);
  book(_h["eta_bar_D"], 5, 1, 2);

  // Table6, T4, F4AB
  book(_h["x_gamma_A"], 6, 1, 1);
  book(_h["x_gamma_B"], 6, 1, 2);

  // Table7, T5, F4CD
  book(_h["x_p_C"], 7, 1, 1);
  book(_h["x_p_D"], 7, 1, 2);

  // Table8, T6, F5,6
  book(_h["x_gamma_bylowEt"], 8, 1, 1);
  book(_h["x_gamma_byhighEt"], 8, 1, 2);

  // Table9, T7, F8AB
  book(_h["cos_theta_A"], 9, 1, 1);
  book(_h["cos_theta_B"], 9, 1, 2);

  // Table10, T7, F8CD
  book(_h["cos_theta_C"], 10, 1, 1);
  book(_h["cos_theta_D"], 10, 1, 2);
}


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

  // DIS Kinematics & Warnings
  const DISKinematics& kin = apply<DISFinalState>(event, "dfs").kinematics();
  if (kin.failed()) vetoEvent;

  // inelasticity cuts
  if (!inRange(kin.y(), 0.1, 0.9)) vetoEvent;

  // Q^2 cuts
  if (kin.Q2() > 1 * GeV2) vetoEvent;

  const int orientation = kin.orientation();

  // Jets
  const Jets jets = apply<FastJets>(event, "jets").jets(cmpMomByEt);

  // Veto event by number of jets
  if (jets.size() < 2) vetoEvent;

  // Define jet numbers
  const Jet& j1 = jets[0];
  const Jet& j2 = jets[1];

  // Cuts by jet energy
  if (j1.Et() < 25 * GeV) vetoEvent;
  if (j2.Et() < 15 * GeV) vetoEvent;

  // Define eta (with orientations)
  const double eta1 = orientation * j1.eta(), eta2 = orientation * j2.eta();

  // Cuts by eta
  if (eta1 < -0.5 || eta1 > 2.5) vetoEvent;
  if (eta2 < -0.5 || eta2 > 2.5) vetoEvent;

  // Invariant Mass
  double mjj = (j1.mom() + j2.mom()).mass();

  //Define Et_mean
  const double Et_mean = 0.5 * (j1.Et() + j2.Et());

  // Define eta_bar
  const double eta_bar = 0.5 * (eta1 + eta2);

  // Define x_gamma
  const double x_gamma = (j1.Et() * exp(-eta1) + j2.Et() * exp(-eta2))
      / (2 * kin.y() * kin.beamLepton().E());

  // Define x_p
  const double x_p = (j1.Et() * exp(eta1) + j2.Et() * exp(eta2)) / (2 * kin.beamHadron().E());

  // Define cos_theta_*
  const double cos_theta = abs(tanh(0.5 * (eta1 - eta2)));

  //fill histos
  _h["mjj"]->fill(mjj / GeV);
  _h["Et_mean"]->fill(Et_mean / GeV);
  _h["Et_max"]->fill(j1.Et() / GeV);

  if (inRange(kin.y(), 0.1, 0.5)) {
    if (inRange(j1.Et(), 25 * GeV, 35 * GeV)) _h["eta_bar_A"]->fill(eta_bar);
    if (inRange(j1.Et(), 35 * GeV, 80 * GeV)) _h["eta_bar_B"]->fill(eta_bar);
  }

  if (inRange(kin.y(), 0.5, 0.9)) {
    if (inRange(j1.Et(), 25 * GeV, 35 * GeV)) _h["eta_bar_C"]->fill(eta_bar);
    if (inRange(j1.Et(), 35 * GeV, 80 * GeV)) _h["eta_bar_D"]->fill(eta_bar);
  }

  if (x_p < 0.1) _h["x_gamma_A"]->fill(x_gamma);
  if (x_p > 0.1) _h["x_gamma_B"]->fill(x_gamma);

  if (x_gamma < 0.8) _h["x_p_C"]->fill(x_p);
  if (x_gamma > 0.8) _h["x_p_D"]->fill(x_p);

  if (inRange(j1.Et(), 25 * GeV, 35 * GeV)) _h["x_gamma_bylowEt"]->fill(x_gamma);
  if (inRange(j1.Et(), 35 * GeV, 80 * GeV)) _h["x_gamma_byhighEt"]->fill(x_gamma);

  if (x_gamma < 0.8) _h["cos_theta_A"]->fill(cos_theta);
  if (x_gamma > 0.8) _h["cos_theta_B"]->fill(cos_theta);

  if (mjj > 65 * GeV) {
    if (x_gamma < 0.8) _h["cos_theta_C"]->fill(cos_theta);
    if (x_gamma > 0.8) _h["cos_theta_D"]->fill(cos_theta);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h, crossSection() / picobarn / sumW());
}

/// @}


/// @name Histograms
/// @{
map<string, Histo1DPtr> _h;
/// @}

};

RIVET_DECLARE_PLUGIN(H1_2002_I581409); } ```