Rivet analyses

title: CMS_2015_I1385107

Underlying event measurement with leading jets at $\sqrt{s} = 2.76$~\TeV

Experiment: CMS (LHC)

Inspire ID: 1385107

Status: VALIDATED

Authors: - Wei Yang Wang - Xavier Janssen

References: none listed

Beams: p+ p+

Beam energies: (1380.0, 1380.0)GeV

Run details: - Requires inclusive inelastic events (non-diffractive and inelastic diffractive). The profile plots require large statistics.

A measurement of the underlying event (UE) activity in proton-proton collisions is performed using events with charged-particle jets produced in the central pseudorapidity region ($|\eta|^\text{jet} < 2$) and with transverse momentum $1 \leq p_T^\text{jet} < 100$~\GeV. The analysis uses a data sample collected at a centre-of-mass energy of 2.76~\TeV with the CMS experiment at the LHC. The UE activity is measured as a function of $p_T^\text{jet}$ in terms of the average multiplicity and scalar sum of transverse momenta of charged particles, with $|\eta| < 2$ and $p_T > 0.5$~\GeV, in the azimuthal region transverse to the highest-$p_T$ jet direction. By further dividing the transverse region into two regions of smaller and larger activity, various components of the UE activity are separated.

Source code:CMS_2015_I1385107.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// CMS UE charged particles vs. leading jet at 2.76 TeV class CMS_2015_I1385107 : public Analysis { public:

/// Constructor
CMS_2015_I1385107()
    : Analysis("CMS_2015_I1385107"),
      ETACUT(2.0),
      AREATOT(2 * ETACUT * 2 * M_PI),
      AREA3(AREATOT / 3.),
      AREA6(AREATOT / 6.) { }


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

  const ChargedFinalState cfs(Cuts::abseta < 2 && Cuts::pT > 500 * MeV);
  declare(cfs, "CFS");

  const ChargedFinalState cfsforjet(Cuts::abseta < 2.5 && Cuts::pT > 500 * MeV);
  const FastJets jetpro(cfsforjet, JetAlg::SISCONE, 0.5);
  declare(jetpro, "Jets");

  book(_h_Nch_TransAVE_vs_pT, 1, 1, 1); // Nch vs. pT_max      (TransAVE)
  book(_h_Sum_TransAVE_vs_pT, 2, 1, 1); // sum(pT) vs. pT_max  (TransAVE)
  book(_h_Nch_TransMAX_vs_pT, 3, 1, 1); // Nch vs. pT_max      (TransMAX)
  book(_h_Sum_TransMAX_vs_pT, 4, 1, 1); // sum(pT) vs. pT_max  (TransMAX)
  book(_h_Nch_TransMIN_vs_pT, 5, 1, 1); // Nch vs. pT_max      (TransMIN)
  book(_h_Sum_TransMIN_vs_pT, 6, 1, 1); // sum(pT) vs. pT_max  (TransMIN)
  book(_h_Nch_TransDIF_vs_pT, 7, 1, 1); // Nch vs. pT_max      (TransDIF)
  book(_h_Sum_TransDIF_vs_pT, 8, 1, 1); // sum(pT) vs. pT_max  (TransDIF)
}


/// Local definition of a signed dphi, for use in differentating L and R trans regions
double signedDeltaPhi(double jetphi, double partphi) {
  double delta = partphi - jetphi;
  while (delta <= -PI) delta += 2 * PI;
  while (delta > PI) delta -= 2 * PI;
  return delta;
}

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

  // Find the lead jet, applying a restriction that the jets must be within |eta| < 2.
  FourMomentum p_lead;
  for (const Jet& j : apply<FastJets>(event, "Jets").jetsByPt(Cuts::abseta < 2.0 && Cuts::pT > 1 * GeV)) {
    p_lead = j.momentum();
    break;
  }
  if (p_lead.isZero()) vetoEvent;
  const double phi_lead = p_lead.phi();
  const double pT_lead = p_lead.pT();

  // Loop on charged particles and separate Left and Right transverse regions
  Particles particles = apply<ChargedFinalState>(event, "CFS").particlesByPt();
  int nch_TransLeft = 0, nch_TransRight = 0;
  double ptSum_TransLeft = 0., ptSum_TransRight = 0.;
  for (const Particle& p : particles) {
    const double dphi = signedDeltaPhi(phi_lead, p.momentum().phi());
    if (!inRange(fabs(dphi), PI / 3, 2 * PI / 3.)) continue; //< only fill trans regions
    if (dphi < 0) {                                          // Transverse Right region
      nch_TransRight += 1;
      ptSum_TransRight += p.pT() / GeV;
    }
    else if (dphi > 0) { // Transverse Left region
      nch_TransLeft += 1;
      ptSum_TransLeft += p.pT() / GeV;
    }
  }

  // Translate to min and max (+sum and diff) Transverse regions
  const int nch_TransMIN = std::min(nch_TransLeft, nch_TransRight);
  const int nch_TransMAX = std::max(nch_TransLeft, nch_TransRight);
  const int nch_TransSUM = nch_TransMAX + nch_TransMIN;
  const int nch_TransDIF = nch_TransMAX - nch_TransMIN;
  //
  const double ptSum_TransMIN = std::min(ptSum_TransLeft, ptSum_TransRight);
  const double ptSum_TransMAX = std::max(ptSum_TransLeft, ptSum_TransRight);
  const double ptSum_TransSUM = ptSum_TransMAX + ptSum_TransMIN;
  const double ptSum_TransDIF = ptSum_TransMAX - ptSum_TransMIN;

  // Fill profiles
  _h_Nch_TransMIN_vs_pT->fill(pT_lead / GeV, 1 / AREA6 * nch_TransMIN);
  _h_Sum_TransMIN_vs_pT->fill(pT_lead / GeV, 1 / AREA6 * ptSum_TransMIN);
  //
  _h_Nch_TransMAX_vs_pT->fill(pT_lead / GeV, 1 / AREA6 * nch_TransMAX);
  _h_Sum_TransMAX_vs_pT->fill(pT_lead / GeV, 1 / AREA6 * ptSum_TransMAX);
  //
  _h_Nch_TransAVE_vs_pT->fill(pT_lead / GeV, 1 / AREA3 * nch_TransSUM);
  _h_Sum_TransAVE_vs_pT->fill(pT_lead / GeV, 1 / AREA3 * ptSum_TransSUM);
  //
  _h_Nch_TransDIF_vs_pT->fill(pT_lead / GeV, 1 / AREA6 * nch_TransDIF);
  _h_Sum_TransDIF_vs_pT->fill(pT_lead / GeV, 1 / AREA6 * ptSum_TransDIF);
}

private:

// Data members like post-cuts event weight counters go here
const double ETACUT, AREATOT, AREA3, AREA6;

/// Histograms
Profile1DPtr _h_Nch_TransAVE_vs_pT, _h_Sum_TransAVE_vs_pT;
Profile1DPtr _h_Nch_TransDIF_vs_pT, _h_Sum_TransDIF_vs_pT;
Profile1DPtr _h_Nch_TransMIN_vs_pT, _h_Sum_TransMIN_vs_pT;
Profile1DPtr _h_Nch_TransMAX_vs_pT, _h_Sum_TransMAX_vs_pT;

};

RIVET_DECLARE_PLUGIN(CMS_2015_I1385107);

} ```