Rivet analyses

title: LHCB_2018_I1665223

Measurement of $pp$ inelastic cross-section at 13 TeV using prompt, long-lived particles in the LHCb fiducial phase-space

Experiment: LHCB (LHC)

Inspire ID: 1665223

Status: VALIDATED

Authors: - Michael Schmelling - Alex Grecu

References: - JHEP 1806 (2018) 100 - DOI:10.1007/JHEP06(2018)100 - arXiv: 1803.10974 - Expt page: LHCb-PAPER-2018-003, CERN-EP-2018-044

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - Proton-proton interactions at 13 TeV centre-of-mass energy. LHCb minimum bias, inelastic events.

LHCb measurement of the inelastic interaction cross-section in proton-proton collisions at $\sqrt{s}=13$ TeV. Events are selected if they contain at least one prompt long-lived charged particle with momentum $p > 2$ GeV$/c$ and pseudorapidity ($\eta$) in the range $2 < \eta < 5$. A particle is long-lived if its proper (mean) lifetime is larger than $0.3 \times 10^{-10}$ s, (proper $c\tau > 9$ mm) and it is prompt if it is produced directly in the $pp$ collision or if none of its ancestors is long-lived. This definition is recommended by the LHC Minimum Bias and Underlying Event working group. Prompt long-lived charged hadrons should be used themselves in vetoing events rather than their charged decay products (e.g. Sigma +/-, Xi and Omega decays are blocked).

Source code:LHCB_2018_I1665223.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {

/// @brief Inelastic xsection in pp collisions at 13 TeV for charged particles in LHCb acceptance class LHCB_2018_I1665223 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2018_I1665223);


/// @name Analysis methods
/// @{

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

  // Register projection
  declare(ChargedFinalState(Cuts::etaIn(ETAMIN, ETAMAX)), "lbCFS");

  // Book histogram
  book(_h_ppInel, 1, 1, 1);
}


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

  // Eliminate non-inelastic events and empty events in LHCb
  const ChargedFinalState& cfs = apply<ChargedFinalState>(event, "lbCFS");
  if (cfs.particles().size() == 0) vetoEvent;

  for (const Particle& myp : cfs.particles()) {
    if (hasLongLivedParent(myp)) continue;
    if (!isLongLivedParticle(myp)) continue;
    // Only particles with p > 2 GeV measured
    if (myp.momentum().p() < PMIN) continue;
    // Histo gets filled only for inelastic events (at least one prompt charged particle)
    _h_ppInel->fill(sqrtS());
    break;
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_ppInel, crossSection() / millibarn / sumOfWeights()); // norm to cross section (one-sided LHCb)
}

/// @}


bool isLongLivedParticle(const Particle& p) {
  // Stable long-lived final-state charged particles in LHCb
  static const int stablePids[9] = {11, 13, 211, 321, 2212, 3112, 3222, 3312, 3334};
  for (int stablePid : stablePids) {
    if (p.abspid() == stablePid) return true;
  }
  return false;
}

bool hasLongLivedParent(const Particle& p) {
  // List of PDG IDs for particle with lifetimes higher than 0.03 ns (3.E-11 s) - long lived particles according to LHC MB&UE WG
  static const int longLivedPids[20] = {3334, 3322, 3312,  3222,      3122, 3112, 2212, 2112, 321, 310,
                                        130,  211,  20022, 480000000, 11,   12,   13,   14,   16,  22};
  for (int longLivedPid : longLivedPids) {
    if (p.hasParentWith(Cuts::abspid == longLivedPid)) return true;
  }
  return false;
}

/// @name Histogram
Histo1DPtr _h_ppInel;

/// Cut constants
const double ETAMIN = 2.0, ETAMAX = 5.0, PMIN = 2.0 * GeV;

};

RIVET_DECLARE_PLUGIN(LHCB_2018_I1665223);

} ```