Rivet analyses

title: CMS_2015_I1346843

Measurement of differential cross-section of FSR photons in $Z$ decays

Experiment: CMS (LHC)

Inspire ID: 1346843

Status: VALIDATED

Authors: - Andrew Kubik - Michael Schmitt

References: - arXiv: 1502.07940

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - $p p \to \mu^+ \mu^- \gamma$+X 7 TeV. These cross sections are given for the fiducial region defined as follows - Leading muon $p_T > 31$ GeV and abs(eta) < 2.4 - Trailing muon $p_T > 9$ GeV and abs(eta) < 2.4 - Photon $p_T > 5$ GeV - Photon abs(eta) < 2.4 but not 1.4 < abs(eta) < 1.6 - Separation between photon and closest muon 0.05 < DeltaR < 3.0 - Di-muon invariant mass 30 < M_mumu < 87 GeV

The differential cross sections for the production of photons in Z to mu+ mu- gamma decays are presented as a function of the transverse energy of the photon and its separation from the nearest muon. The data for these measurements were collected with the CMS detector and correspond to an integrated luminosity of 4.7 inverse femtobarns of pp collisions at sqrt(s) = 7 TeV delivered by the CERN LHC.

Source code:CMS_2015_I1346843.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedLeptons.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/NeutralFinalState.hh"

include "Rivet/Projections/PromptFinalState.hh"

namespace Rivet {

/// Differential cross-section of FSR photons in Z decays class CMS_2015_I1346843 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2015_I1346843);

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

  Cut c_photons = Cuts::pT >= 5 * GeV && Cuts::abseta < 2.5 && !(Cuts::absetaIn(1.4, 1.6));
  PromptFinalState photons(Cuts::abspid == PID::PHOTON && c_photons, TauDecaysAs::PROMPT,
                           MuDecaysAs::PROMPT);
  declare(photons, "PHOTONFS");

  Cut c_muons = Cuts::pT > 9 * GeV && Cuts::abseta < 2.4;
  PromptFinalState muons(Cuts::abspid == PID::MUON && c_muons);
  declare(muons, "MUFS");

  book(_h["pho_et"], 1, 1, 1);       // photon transverse energy
  book(_h["pho_et_wide"], 1, 2, 1);  // photon transverse energy (0.5 < dr < 3.0)
  book(_h["pho_et_close"], 1, 3, 1); // photon transverse energy (0.05 < dr < 0.5)
  book(_h["pho_et_lqt"], 1, 4, 1);   // photon transverse energy (q_T < 10)
  book(_h["pho_et_hqt"], 1, 5, 1);   // photon transverse energy (q_T > 50)
  book(_h["pho_dr"], 2, 1, 1);       // delta_R
  book(_h["pho_dr_lqt"], 2, 2, 1);   // delta_R (q_T < 10)
  book(_h["pho_dr_hqt"], 2, 3, 1);   // delta_R  (q_T > 50)
}


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

  const Particles muons = apply<PromptFinalState>(event, "MUFS").particlesByPt();

  if (muons.size() < 2) vetoEvent;
  if (muons[0].pT() < 31 * GeV) vetoEvent;
  if (muons[0].charge() * muons[1].charge() > 0) vetoEvent;
  const double mZ = (muons[0].momentum() + muons[1].momentum()).mass();
  if (!inRange(mZ, 30 * GeV, 87 * GeV)) vetoEvent;

  const Particles photons = apply<PromptFinalState>(event, "PHOTONFS").particlesByPt();
  // We want the photon with the highest pT that does not come from a decay
  for (const Particle& p : photons) {

    const double dR = std::min(deltaR(p, muons[0]), deltaR(p, muons[1]));
    if (!inRange(dR, 0.05, 3.0)) continue;

    // Calculate the three-body (mu,mu,gamma) transverse momentum
    const double qT = (muons[0].mom() + muons[1].mom() + p.mom()).pT();

    // Fill the analysis histograms
    _h["pho_et"]->fill(p.pT() / GeV, 1.0);
    _h["pho_dr"]->fill(dR, 1.0);

    _h[(dR <= 0.5 ? "pho_et_close" : "pho_et_wide")]->fill(p.pT() / GeV, 1.0);

    if (qT / GeV < 10.) {
      _h["pho_et_lqt"]->fill(p.pT() / GeV, 1.0);
      _h["pho_dr_lqt"]->fill(dR, 1.0);
    }

    if (qT / GeV > 50.) {
      _h["pho_et_hqt"]->fill(p.pT() / GeV, 1.0);
      _h["pho_dr_hqt"]->fill(dR, 1.0);
    }

    break; // Exit the loop since we found the highest pT lepton already
  }
}


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

private:

map<std::string, Histo1DPtr> _h;

};

RIVET_DECLARE_PLUGIN(CMS_2015_I1346843);

} ```