Rivet analyses

title: D0_2006_I698784

Inclusive isolated photon cross-section, differential in pT(gamma)

Experiment: D0 (Tevatron Run 2)

Inspire ID: 698784

Status: VALIDATED

Authors: - Andy Buckley - Gavin Hesketh - Frank Siegert

References: - Phys.Lett.B639:151-158,2006, Erratum-ibid.B658:285-289,2008 - DOI: 10.1016/j.physletb.2006.04.048 - arXiv: hep-ex/0511054

Beams: p- p+

Beam energies: (980.0, 980.0)GeV

Run details: - ppbar collisions at $\sqrt{s} = 1960$ GeV. Requires gamma + jet (q,qbar,g) hard processes, which for Pythia 6 means MSEL=10 for with MSUB indices 14, 18, 29, 114, 115 enabled.

Measurement of differential cross section for inclusive production of isolated photons in p pbar collisions at $\sqrt{s} = 1.96$ TeV with the D\O detector at the Fermilab Tevatron collider. The photons span transverse momenta 23--300 GeV and have pseudorapidity $|\eta| < 0.9$. Isolated direct photons are probes of pQCD via the annihilation ($q \bar{q} -> \gamma g$) and quark-gluon Compton scattering ($q g -> \gamma q$) processes, the latter of which is also sensitive to the gluon PDF. The initial state radiation / resummation formalisms are sensitive to the resulting photon pT spectrum

Source code:D0_2006_I698784.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/LeadingParticlesFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {

/// @brief D0 inclusive isolated photon cross-section vs. \f$ p_\perp(gamma) \f$. /// /// @author Andy Buckley /// @author Gavin Hesketh class D0_2006_I698784 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(D0_2006_I698784);


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

void init() {
  // General FS for photon isolation
  FinalState fs;
  declare(fs, "AllFS");

  // Get leading photon
  LeadingParticlesFinalState photonfs(FinalState((Cuts::etaIn(-0.9, 0.9) && Cuts::pT >= 23.0 * GeV)));
  photonfs.addParticleId(PID::PHOTON);
  declare(photonfs, "LeadingPhoton");

  // Book histograms
  book(_h_pTgamma, 1, 1, 1);
}


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

  // Get the photon
  const FinalState& photonfs = apply<FinalState>(event, "LeadingPhoton");
  if (photonfs.particles().size() != 1) {
    vetoEvent;
  }
  const FourMomentum photon = photonfs.particles().front().momentum();

  // Isolate photon by ensuring that a 0.4 cone around it contains less than 10% of the photon's energy
  double E_P = photon.E();
  double eta_P = photon.eta();
  double phi_P = photon.phi();
  double econe = 0.0;
  for (const Particle& p : apply<FinalState>(event, "AllFS").particles()) {
    if (deltaR(eta_P, phi_P, p.eta(), p.phi()) < 0.4) {
      econe += p.E();
      if (econe / E_P > 1.1) {
        vetoEvent;
      }
    }
  }

  // Fill histo
  _h_pTgamma->fill(photon.pT());
}


// Finalize
void finalize() {
  const double lumi_gen = sumOfWeights() / crossSection() / picobarn;
  // Divide by effective lumi, plus rapidity bin width of 1.8
  scale(_h_pTgamma, 1 / lumi_gen * 1 / 1.8);
}

/// @}

private:

/// @name Histograms
/// @{
Histo1DPtr _h_pTgamma;
/// @}

};

RIVET_DECLARE_ALIASED_PLUGIN(D0_2006_I698784, D0_2006_S6438750);

} ```

Aliases: - D0_2006_S6438750