Rivet analyses

title: LHCB_2012_I1208102

Differential cross-sections of $\mathrm{Z}/\gamma^ \to e^{+}e^{-}$ vs rapidity and $\phi^$

Experiment: LHCb (LHC)

Inspire ID: 1208102

Status: VALIDATED

Authors: - Ana Elena Dumitriu - Marek Sirendi - David Ward - Alex Grecu

References: - J. High Energy Phys. 02 (2013) 106 - DOI: 10.1007/JHEP02(2013)106 - arXiv: 1212.4620

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - $\mathrm{Z}/\gamma^* \to e^{+}e^{-}_$ decays with di-lepton invariant mass $> 40$ GeV/$c^2$ produced in $pp$ collisions at $\sqrt{s}=7$ TeV.

Measurement of the $pp \to \mathrm{Z}^0$ cross-section in the $\mathrm{Z}/\gamma \to e^{+}e^{-}$ mode at $\sqrt{s} = 7$ TeV. Daughter electrons are required to have $p_T > 20$ GeV/$c$, $2 < \eta < 4.5$ and the dielectron invariant mass in range 60-120 GeV/$c^2$. The cross-section is given as a function of $Z$ rapidity and an angular variable ($\phi^*$) closely related to $Z$ transverse momentum (derived from the lepton pseudorapidity and azimuthal angle differences). For event generators implementing cross-section QCD corrections only at LO the distributions are normalized to the cross-section measured in data $76.0 \pm 0.8 \pm 2.0 \pm 2.6 \pm 0.4$ pb, where the first uncertainty is statistical, the second is systematic, the third is due to luminosity uncertainty and the fourth to FSR corrections.

Source code:LHCB_2012_I1208102.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DileptonFinder.hh"

namespace Rivet {

/// Differential cross-sections of $\mathrm{Z}/\gamma^ \to e^{+}e^{-}$ vs rapidity and $\phi^$ class LHCB_2012_I1208102 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2012_I1208102);


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

/// Book histograms
void init() {
  DileptonFinder zeefinder(91.2 * GeV, 0.1,
                           Cuts::etaIn(2.0, 4.5) && Cuts::pT > 20 * GeV && Cuts::abspid == PID::ELECTRON,
                           Cuts::massIn(60 * GeV, 120 * GeV));
  declare(zeefinder, "ZeeFinder");

  book(_h_sigma_vs_y, 2, 1, 1);
  book(_h_sigma_vs_phi, 3, 1, 1);
}


/// Do the analysis
void analyze(const Event& e) {
  const DileptonFinder& zeefinder = apply<DileptonFinder>(e, "ZeeFinder");
  if (zeefinder.empty()) vetoEvent;
  if (zeefinder.bosons().size() > 1)
    MSG_WARNING("Found multiple (" << zeefinder.bosons().size() << ") Z -> e+ e- decays!");

  // Z momenta
  const FourMomentum zee = zeefinder.bosons()[0].momentum();

  if (zeefinder.constituents().size() < 2) vetoEvent;

  const Particle pozitron = zeefinder.constituents()[0];
  const Particle electron = zeefinder.constituents()[1];

  // Calculation of the angular variable
  const double diffphi = deltaPhi(pozitron, electron);
  const double diffpsd = deltaEta(pozitron, electron);
  const double accphi = M_PI - diffphi;
  const double angular = tan(accphi / 2) / cosh(diffpsd / 2);

  // Fill histograms
  _h_sigma_vs_y->fill(zee.rapidity());
  _h_sigma_vs_phi->fill(angular);
}


/// Finalize
void finalize() {
  const double xs = crossSection() / picobarn;
  scale(_h_sigma_vs_y, xs / sumOfWeights());
  scale(_h_sigma_vs_phi, xs / sumOfWeights());
}

/// @}

private:

/// @name Histograms
/// @{
Histo1DPtr _h_sigma_vs_y, _h_sigma_vs_phi;
/// @}

};

RIVET_DECLARE_PLUGIN(LHCB_2012_I1208102);

} ```