Rivet analyses

title: CMS_2018_I1708620

Energy density vs pseudorapidity in proton-proton collisions at $\sqrt{s} = 13$ TeV

Experiment: CMS (LHC)

Inspire ID: 1708620

Status: VALIDATED

Authors: - Deniz Sunar Cerci - Sercan Sen - Salim Cerci - Caglar Zorbilmez - Ilknur Hos

References: - Expt page: CMS-FSQ-15-006 - CERN-EP-2018-308 - arXiv: 1812.04095

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - Inelastic, single-diffractive and non-single diffractive events at $\sqrt{s} = 13$~TeV.

A measurement of the energy density in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV is presented. The data have been recorded with the CMS experiment at the LHC during low luminosity operations in 2015. The energy density is studied as a function of pseudorapidity in the ranges $-6.6 < \eta < -5.2$ and $3.15 < |\eta| < 5.20$. The results are compared with the predictions of several models. All the models considered suggest a different shape of the pseudorapidity dependence compared to that observed in the data. A comparison with LHC proton-proton collision data at $\sqrt{s} = 0.9$ and 7 TeV confirms the compatibility of the data with the hypothesis of limiting fragmentation.

Source code:CMS_2018_I1708620.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {

/// Forward energy flow at 13 TeV with CMS /// /// @note Rivet 3 conversion by A Buckley class CMS_2018_I1708620 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2018_I1708620);


/// Initialise
void init() {

  declare(FinalState(), "FS");
  const ChargedFinalState cfsBSCplus(Cuts::eta > 3.9 && Cuts::eta < 4.4);
  declare(cfsBSCplus, "cfsBSCplus");
  const ChargedFinalState cfsBSCminus(Cuts::eta > -4.4 && Cuts::eta < -3.9);
  declare(cfsBSCminus, "cfsBSCminus");

  book(_noe_inel, "TMP/Ninel");
  book(_noe_nsd, "TMP/Nnsd");
  book(_noe_bsc, "TMP/Nbsc");
  book(_noe_sd, "TMP/Nsd");
  book(_noe_nsd_sd, "TMP/Nnsdsd");

  book(_h_inel, 1, 1, 1);
  book(_h_nsd, 2, 1, 1);
  book(_h_et, 3, 1, 1);
  book(_h_sd, 4, 1, 1);
}


void analyze(const Event& event) {

  const ChargedFinalState& cfsBSCplus = apply<ChargedFinalState>(event, "cfsBSCplus");
  const ChargedFinalState& cfsBSCminus = apply<ChargedFinalState>(event, "cfsBSCminus");
  const bool bscplus = !cfsBSCplus.empty();
  const bool bscminus = !cfsBSCminus.empty();

  // Find final-state particles
  const FinalState& fs = apply<FinalState>(event, "FS");
  // const Particles particlesByRapidity = fs.particlesByPt();
  // sortBy(particlesByRapidity, cmpMomByRap);
  const Particles particlesByRapidity = fs.particles(cmpMomByRap);
  const size_t num_particles = particlesByRapidity.size();

  // Find gaps, and choose the middle one as the event gap centre
  vector<double> gaps, midpoints;
  for (size_t ip = 1; ip < num_particles; ++ip) {
    const Particle& p1 = particlesByRapidity[ip - 1];
    const Particle& p2 = particlesByRapidity[ip];
    const double gap = p2.rapidity() - p1.rapidity();
    const double mid = (p2.rapidity() + p1.rapidity()) / 2;
    gaps.push_back(gap);
    midpoints.push_back(mid);
  }
  const size_t imid = std::distance(gaps.begin(), max_element(gaps.begin(), gaps.end()));
  const double gapcenter = midpoints[imid];

  // Assign particles to sides and compute Mx, My
  FourMomentum v4mx, v4my;
  for (const Particle& p : particlesByRapidity) {
    (p.rapidity() > gapcenter ? v4mx : v4my) += p.momentum();
  }
  const double mx = v4mx.mass();
  const double my = v4my.mass();

  // Compute xi variables
  const double xix = sqr(mx / (sqrtS() / GeV));
  const double xiy = sqr(my / (sqrtS() / GeV));
  const double xi_sd = max(xix, xiy);

  // Compute if inelastic, and other variables
  const bool inel = (xi_sd > 1e-6);
  if (inel) _noe_inel->fill();
  const bool bsc = (bscplus && bscminus);
  if (bsc) _noe_bsc->fill(); ///< @todo Not re-entry safe: FIX

  // Count/histogram backward and forward Et
  static const double YBEAM = 9.54;
  int nplus = 0, nminus = 0;
  for (const Particle& p : particlesByRapidity) {
    const double eta = p.eta();
    if (!p.isVisible()) continue;
    if (inRange(eta, 2.866, 5.205)) nplus += 1;
    if (inRange(eta, -5.205, -2.866)) nminus += 1;
    if (bsc) _h_et->fill(eta - YBEAM, p.Et() / GeV);
  }

  // Categorise as NSD
  const bool nsd = (nminus > 0 && nplus > 0);
  if (nsd) _noe_nsd->fill();

  // Histogram
  for (const Particle& p : particlesByRapidity) {
    if (inel) _h_inel->fill(p.abseta(), p.E() / GeV);
    if (nsd) _h_nsd->fill(p.abseta(), p.E() / GeV);
  }

  // SD selection
  static const double ETAMIN = 3.152;
  static const double ETAMAX = 5.205;
  static const double EMIN = 5 * GeV;
  bool stableParticleEnergyCutMinus = false, stableParticleEnergyCutPlus = false;
  for (const Particle& p : particlesByRapidity) {
    if (p.E() < EMIN) continue;
    if (inRange(p.eta(), -ETAMAX, -ETAMIN)) stableParticleEnergyCutMinus = true;
    if (inRange(p.eta(), ETAMIN, ETAMAX)) stableParticleEnergyCutPlus = true;
  }

  // Select SD-enhanced events with the following condition
  const bool sd = (stableParticleEnergyCutPlus != stableParticleEnergyCutMinus); //< bool XOR
  if (sd) {
    _noe_sd->fill();
    for (const Particle& p : particlesByRapidity) {
      if (inRange(p.abseta(), ETAMIN, ETAMAX)) {
        if (stableParticleEnergyCutPlus && p.eta() > 0) _h_sd->fill(p.abseta(), p.E() / GeV);
        if (stableParticleEnergyCutMinus && p.eta() < 0) _h_sd->fill(p.abseta(), p.E() / GeV);
      }
      else { // CASTOR
        _h_sd->fill(p.abseta(), p.E() / GeV / 2);
      }
    }
  }

  // Count how many are NSD and SD
  if (nsd && sd) _noe_nsd_sd->fill();
}


void finalize() {
  scale(_h_inel, 0.5 / _noe_inel->sumW());
  scale(_h_nsd, 0.5 / _noe_nsd->sumW());
  scale(_h_et, 1 / _noe_bsc->sumW());
  scale(_h_sd, 1 / _noe_sd->sumW());
  MSG_DEBUG("Number of events of INEL: " << _noe_inel->effNumEntries());
  MSG_DEBUG("Number of events of NSD: " << _noe_nsd->effNumEntries());
  MSG_DEBUG("Number of events of SD: " << _noe_sd->effNumEntries());
  MSG_DEBUG("Number of events of NSD and SD contribution: " << _noe_nsd_sd->effNumEntries());
}


Histo1DPtr _h_inel, _h_nsd, _h_et, _h_sd;
CounterPtr _noe_inel, _noe_nsd, _noe_bsc, _noe_sd, _noe_nsd_sd;

};

RIVET_DECLARE_PLUGIN(CMS_2018_I1708620);

} ```