Rivet analyses

title: CMS_2013_I1256943

Cross-section and angular correlations in $Z$ boson with $b$-hadrons events at $\sqrt{s} = 7$ TeV

Experiment: CMS (LHC)

Inspire ID: 1256943

Status: VALIDATED

Authors: - Lorenzo Viliani - Piergiulio Lenzi

References: - 10.1007 / JHEP12(2013)039 - arXiv: 1310.1349 - CERN-PH-EP-2013-153 - Expt page: CMS-EWK-11-015

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - $pp$ collisions with $\sqrt{s} = 7$ TeV. Selection of events with exactly two $b$-hadrons and a lepton pair from the $Z$ boson decay. Each lepton has $p_T > 20$ GeV and $|\eta| < 2.4$ and the dilepton invariant mass is $81 < M_{\ell\ell} < 101$ GeV. The $b$-hadrons have $p_T > 15$ GeV and $|\eta| < 2$. The differential cross sections are measured for $p_T > 0$ and $p_T > 50$ GeV.

A study of proton-proton collisions in which two $b$-hadrons are produced in association with a $Z$ boson is reported. The collisions were recorded at a centre-of-mass energy of 7 TeV with the CMS detector at the LHC, for an integrated luminosity of 5.2/fb. The $b$-hadrons are identified by means of displaced secondary vertices, without the use of reconstructed jets, permitting the study of $b$-hadron pair production at small angular separation. Differential cross sections are presented as a function of the angular separation of the $b$-hadrons and the $Z$ boson. In addition, inclusive measurements are presented. For both the inclusive and differential studies,different ranges of $Z$ boson momentum are considered.

Source code:CMS_2013_I1256943.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DileptonFinder.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// CMS cross-section and angular correlations in Z boson + b-hadrons events at 7 TeV class CMS_2013_I1256943 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2013_I1256943);


/// Add projections and book histograms
void init() {
  book(_sumW, "sumW");
  book(_sumW50, "sumW50");
  book(_sumWpT, "sumWpT");

  //FinalState fs(Cuts::abseta < 2.4 && Cuts::pT > 20*GeV); //< likely wrong for dressing inputs
  UnstableParticles ufs(Cuts::abseta < 2 && Cuts::pT > 15 * GeV);
  declare(ufs, "UFS");

  Cut zetacut = Cuts::abseta < 2.4;
  DileptonFinder zfindermu(91.2 * GeV, 0.1, zetacut && Cuts::pT > 20 * GeV && Cuts::abspid == PID::MUON,
                           Cuts::massIn(81 * GeV, 101 * GeV));
  declare(zfindermu, "DileptonFinderMu");

  DileptonFinder zfinderel(91.2 * GeV, 0.1,
                           zetacut && Cuts::pT > 20 * GeV && Cuts::abspid == PID::ELECTRON,
                           Cuts::massIn(81 * GeV, 101 * GeV));
  declare(zfinderel, "DileptonFinderEl");


  // Histograms in non-boosted region of Z pT
  book(_h_dR_BB, 1, 1, 1);
  book(_h_dphi_BB, 2, 1, 1);
  book(_h_min_dR_ZB, 3, 1, 1);
  book(_h_A_ZBB, 4, 1, 1);

  // Histograms in boosted region of Z pT (pT > 50 GeV)
  book(_h_dR_BB_boost, 5, 1, 1);
  book(_h_dphi_BB_boost, 6, 1, 1);
  book(_h_min_dR_ZB_boost, 7, 1, 1);
  book(_h_A_ZBB_boost, 8, 1, 1);

  book(_h_min_ZpT, 9, 1, 1);
}


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

  const UnstableParticles& ufs = apply<UnstableParticles>(e, "UFS");
  const DileptonFinder& zfindermu = apply<DileptonFinder>(e, "DileptonFinderMu");
  const DileptonFinder& zfinderel = apply<DileptonFinder>(e, "DileptonFinderEl");

  // Look for a Z --> mu+ mu- event in the final state
  if (zfindermu.empty() && zfinderel.empty()) vetoEvent;

  const Particles& z = !zfindermu.empty() ? zfindermu.bosons() : zfinderel.bosons();
  const bool is_boosted = (z[0].pT() > 50 * GeV);

  // Loop over the unstable particles
  vector<FourMomentum> Bmom;
  for (const Particle& p : ufs.particles()) {
    const PdgId pid = p.pid();

    // Look for particles with a bottom quark
    if (PID::hasBottom(pid)) {

      bool good_B = false;
      ConstGenParticlePtr pgen = p.genParticle();
      ConstGenVertexPtr vgen = pgen->end_vertex();

      // Loop over the decay products of each unstable particle, looking for a b-hadron pair
      /// @todo Avoid HepMC API
      for (ConstGenParticlePtr it : HepMCUtils::particles(vgen, Relatives::CHILDREN)) {
        // If the particle produced has a bottom quark do not count it and go to the next loop cycle.
        if (!(PID::hasBottom(it->pdg_id()))) {
          good_B = true;
          continue;
        }
        else {
          good_B = false;
          break;
        }
      }
      if (good_B) Bmom.push_back(p.momentum());
    }
    else
      continue;
  }

  // If there are more than two B's in the final state veto the event
  if (Bmom.size() != 2) vetoEvent;

  // Calculate the observables
  double dphiBB = deltaPhi(Bmom[0], Bmom[1]);
  double dRBB = deltaR(Bmom[0], Bmom[1]);

  const FourMomentum& pZ = z[0].momentum();
  const bool closest_B = (deltaR(pZ, Bmom[0]) < deltaR(pZ, Bmom[1]));
  const double mindR_ZB = closest_B ? deltaR(pZ, Bmom[0]) : deltaR(pZ, Bmom[1]);
  const double maxdR_ZB = closest_B ? deltaR(pZ, Bmom[1]) : deltaR(pZ, Bmom[0]);
  const double AZBB = (maxdR_ZB - mindR_ZB) / (maxdR_ZB + mindR_ZB);

  // Fill the histograms in the non-boosted region
  _h_dphi_BB->fill(dphiBB);
  _h_dR_BB->fill(dRBB);
  _h_min_dR_ZB->fill(mindR_ZB);
  _h_A_ZBB->fill(AZBB);
  _sumW->fill();
  _sumWpT->fill();

  // Fill the histograms in the boosted region
  if (is_boosted) {
    _sumW50->fill();
    _h_dphi_BB_boost->fill(dphiBB);
    _h_dR_BB_boost->fill(dRBB);
    _h_min_dR_ZB_boost->fill(mindR_ZB);
    _h_A_ZBB_boost->fill(AZBB);
  }

  // Fill Z pT (cumulative) histogram
  _h_min_ZpT->fill(0);
  if (pZ.pT() > 40 * GeV) {
    _sumWpT->fill();
    _h_min_ZpT->fill(40);
  }
  if (pZ.pT() > 80 * GeV) {
    _sumWpT->fill();
    _h_min_ZpT->fill(80);
  }
  if (pZ.pT() > 120 * GeV) {
    _sumWpT->fill();
    _h_min_ZpT->fill(120);
  }

  Bmom.clear();
}


/// Finalize
void finalize() {

  // Normalize excluding overflow bins (d'oh)
  normalize(_h_dR_BB, 0.7 * crossSection() / picobarn * dbl(*_sumW) / sumOfWeights(),
            false); // d01-x01-y01
  normalize(_h_dphi_BB, 0.53 * crossSection() / picobarn * dbl(*_sumW) / sumOfWeights(),
            false); // d02-x01-y01
  normalize(_h_min_dR_ZB, 0.84 * crossSection() / picobarn * dbl(*_sumW) / sumOfWeights(),
            false); // d03-x01-y01
  normalize(_h_A_ZBB, 0.2 * crossSection() / picobarn * dbl(*_sumW) / sumOfWeights(),
            false); // d04-x01-y01

  normalize(_h_dR_BB_boost, 0.84 * crossSection() / picobarn * dbl(*_sumW50) / sumOfWeights(),
            false); // d05-x01-y01
  normalize(_h_dphi_BB_boost, 0.63 * crossSection() / picobarn * dbl(*_sumW50) / sumOfWeights(),
            false); // d06-x01-y01
  normalize(_h_min_dR_ZB_boost, 1 * crossSection() / picobarn * dbl(*_sumW50) / sumOfWeights(),
            false); // d07-x01-y01
  normalize(_h_A_ZBB_boost, 0.25 * crossSection() / picobarn * dbl(*_sumW50) / sumOfWeights(),
            false); // d08-x01-y01

  normalize(_h_min_ZpT, 40 * crossSection() / picobarn * dbl(*_sumWpT) / sumOfWeights(),
            false); // d09-x01-y01
}

private:

/// @name Weight counters
/// @{
CounterPtr _sumW, _sumW50, _sumWpT;
/// @}

/// @name Histograms
/// @{
Histo1DPtr _h_dphi_BB, _h_dR_BB, _h_min_dR_ZB, _h_A_ZBB;
Histo1DPtr _h_dphi_BB_boost, _h_dR_BB_boost, _h_min_dR_ZB_boost, _h_A_ZBB_boost, _h_min_ZpT;
/// @}

};

RIVET_DECLARE_PLUGIN(CMS_2013_I1256943);

} ```