Rivet analyses

title: CMS_2013_I1258128

Rapidity distributions in exclusive $Z$ + jet and $\gamma$ + jet events in $pp$ collisions at $\sqrt{s} = 7$ TeV

Experiment: CMS (LHC)

Inspire ID: 1258128

Status: VALIDATED

Authors: - Steve Linn - Shin-Shan Eiko Yu - Anil Sing Pratap - Lovedeep Kaur Saini - Kittikul Kovitanggoon - Luis Lebolo - Vanessa Gaultney Werner - Yun-Ju Lu - Syue-Wei Li - Yu-Hsiang Chang - Sung-Won Lee - Pete E.C. Markowitz - Darko Mekterovic - Jorge Rodriguez - Bhawan Uppal

References: - arXiv: 1310.3082 - https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSMP12004 - Submitted to Phys. Rev. Lett

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - Run MC generators with $Z$ decaying to leptonic modes + jets and photon + jets at 7 TeV centre-of-mass energy.

Rapidity distributions are presented for events containing either a $Z$ boson or a photon in association with a single jet in proton-proton collisions produced at the CERN LHC. The data, collected with the CMS detector at $\sqrt{s} = 7$ TeV, correspond to an integrated luminosity of 5.0/fb. The individual rapidity distributions of the boson and the jet are consistent within 5\% with expectations from perturbative QCD. However, QCD predictions for the sum and the difference in rapidities of the two final-state objects show significant discrepancies with CMS data. In particular, next-to-leading-order QCD calculations, and two Monte Carlo event generators using different methods to merge matrix-element partons with evolved parton showers, appear inconsistent with the data as well as with each other.

Source code:CMS_2013_I1258128.cc

```c++

include "Rivet/Analysis.hh"

include "Rivet/Projections/DileptonFinder.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/LeadingParticlesFinalState.hh"

include "Rivet/Projections/Thrust.hh"

namespace Rivet {

/// CMS Z rapidity measurement class CMS_2013_I1258128 : public Analysis { public:

// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2013_I1258128);


void init() {

  // Z finders for electrons and muons
  Cut cuts = Cuts::abseta < 2.1 && Cuts::pT > 20 * GeV;
  const DileptonFinder zfe(91.2 * GeV, 0.1, cuts && Cuts::abspid == PID::ELECTRON,
                           Cuts::massIn(76 * GeV, 106 * GeV));
  const DileptonFinder zfm(91.2 * GeV, 0.1, cuts && Cuts::abspid == PID::MUON,
                           Cuts::massIn(76 * GeV, 106 * GeV));
  declare(zfe, "ZFE");
  declare(zfm, "ZFM");

  // Try to get the leading photon
  LeadingParticlesFinalState photonfs(FinalState(Cuts::abseta < 2.5 && Cuts::pT > 40 * GeV));
  photonfs.addParticleId(PID::PHOTON);
  declare(photonfs, "LeadingPhoton");

  // Jets
  const FastJets jets(FinalState(Cuts::abseta < 5), JetAlg::ANTIKT, 0.5);
  declare(jets, "JETS");

  // Histograms
  book(_hist1YZ, 1, 1, 1);
  book(_hist1YJet, 2, 1, 1);
  book(_hist1YSum, 3, 1, 1);
  book(_hist1YDif, 4, 1, 1);
  book(_hist2YPhoton, 5, 1, 1);
  book(_hist2YJet, 6, 1, 1);
  book(_hist2YSum, 7, 1, 1);
  book(_hist2YDif, 8, 1, 1);
}


void makeZCut(const Event& event) {
  // Apply the Z finders and veto if no Z found
  const DileptonFinder& zfe = apply<DileptonFinder>(event, "ZFE");
  const DileptonFinder& zfm = apply<DileptonFinder>(event, "ZFM");
  if (zfe.empty() && zfm.empty()) vetoEvent;

  // Choose the Z candidate
  const Particles& z = (!zfm.empty()) ? zfm.bosons() : zfe.bosons();
  const Particles& clusteredConstituents = (!zfm.empty()) ? zfm.constituents() : zfe.constituents();

  // Insist that the Z is in a high-pT (boosted) regime
  if (z[0].pT() < 40 * GeV) return;

  // Build the jets
  const FastJets& jetfs = apply<FastJets>(event, "JETS");
  Jets jets = jetfs.jetsByPt(Cuts::pT > 30 * GeV && Cuts::abseta < 2.4);
  if (jets.empty()) return;

  // Clean the jets against the lepton candidates with a DeltaR cut of 0.5
  vector<const Jet*> cleanedJets;
  for (const Jet& j : jets) {
    bool isolated = true;
    for (const Particle& p : clusteredConstituents) {
      if (deltaR(p, j) < 0.5) {
        isolated = false;
        break;
      }
    }
    if (isolated) cleanedJets.push_back(&j);
  }
  // Require exactly 1 isolated jet
  if (cleanedJets.size() != 1) return;

  // Fill histos
  const double yz = z[0].rapidity();
  const double yjet = cleanedJets[0]->momentum().rapidity();
  _hist1YZ->fill(fabs(yz));
  _hist1YJet->fill(fabs(yjet));
  _hist1YSum->fill(0.5 * fabs(yz + yjet));
  _hist1YDif->fill(0.5 * fabs(yz - yjet));
}


void makePhotonCut(const Event& event) {
  // Get the photon
  const FinalState& photonfs = apply<FinalState>(event, "LeadingPhoton");
  if (photonfs.particles().size() < 1) return;
  const Particle& photon = photonfs.particles().front();
  if (photon.pT() < 40 * GeV) return;
  if (fabs(photon.eta()) > 1.4442) return;

  // Build the jets
  const FastJets& jetfs = apply<FastJets>(event, "JETS");
  Jets jets = jetfs.jetsByPt(Cuts::pT > 30 * GeV && Cuts::abseta < 2.4);
  if (jets.empty()) return;

  // Clean the jets against the photon candidate with a DeltaR cut of 0.5
  vector<const Jet*> cleanedJets;
  for (const Jet& j : jets)
    if (deltaR(photon, j) > 0.5) cleanedJets.push_back(&j);
  // Require exactly 1 jet
  if (cleanedJets.size() != 1) return;

  // Fill histos
  const double ypho = photon.rapidity();
  const double yjet = cleanedJets[0]->momentum().rapidity();
  _hist2YPhoton->fill(fabs(ypho));
  _hist2YJet->fill(fabs(yjet));
  _hist2YSum->fill(0.5 * fabs(ypho + yjet));
  _hist2YDif->fill(0.5 * fabs(ypho - yjet));
}


void analyze(const Event& event) {
  makeZCut(event);
  makePhotonCut(event);
}


void finalize() {
  normalizeByContents(_hist1YZ);
  normalizeByContents(_hist1YJet);
  normalizeByContents(_hist1YSum);
  normalizeByContents(_hist1YDif);
  normalizeByContents(_hist2YPhoton);
  normalizeByContents(_hist2YJet);
  normalizeByContents(_hist2YSum);
  normalizeByContents(_hist2YDif);
}


// The CMS normalization in this analysis is that the sum over bin contents
// is equal to 1. This function normalizes to area = area*bin_width.  /
// @note This is a strange definition... why?
void normalizeByContents(Histo1DPtr h) {
  normalize(h, h->bin(1).xWidth());
}

private:

Histo1DPtr _hist1YZ, _hist1YJet, _hist1YSum, _hist1YDif;
Histo1DPtr _hist2YPhoton, _hist2YJet, _hist2YSum, _hist2YDif;

};

RIVET_DECLARE_PLUGIN(CMS_2013_I1258128);

} ```