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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
  • 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
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/ChargedFinalState.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief Inelastic xsection in pp collisions at 13 TeV for charged particles in LHCb acceptance
 9  class LHCB_2018_I1665223 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2018_I1665223);
14
15
16    /// @name Analysis methods
17    //@{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21
22      // Register projection
23      declare(ChargedFinalState(Cuts::etaIn(ETAMIN, ETAMAX)), "lbCFS");
24
25      // Book histogram
26      book(_h_ppInel, 1, 1, 1);
27    }
28
29
30    /// Perform the per-event analysis
31    void analyze(const Event& event) {
32
33      // Eliminate non-inelastic events and empty events in LHCb
34      const ChargedFinalState& cfs = apply<ChargedFinalState>(event, "lbCFS");
35      if (cfs.particles().size() == 0) vetoEvent;
36
37      for (const Particle& myp : cfs.particles()) {
38        if (hasLongLivedParent(myp)) continue;
39        if (!isLongLivedParticle(myp)) continue;
40        // Only particles with p > 2 GeV measured
41        if (myp.momentum().p() < PMIN) continue;
42        // Histo gets filled only for inelastic events (at least one prompt charged particle)
43        _h_ppInel->fill(sqrtS());
44        break;
45      }
46    }
47
48
49    /// Normalise histograms etc., after the run
50    void finalize() {
51      scale(_h_ppInel, crossSection()/millibarn/sumOfWeights()); // norm to cross section (one-sided LHCb)
52    }
53
54    //@}
55
56
57  	bool isLongLivedParticle(const Particle& p) {
58  		// Stable long-lived final-state charged particles in LHCb
59  		static const int stablePids[9] = {11,13,211,321,2212,3112,3222,3312,3334};
60  		for (int stablePid : stablePids) {
61          if (p.abspid() == stablePid) return true;
62  		}
63  		return false;
64  	}
65
66    bool hasLongLivedParent(const Particle& p) {
67      // 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
68      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};
69      for (int longLivedPid : longLivedPids) {
70        if (p.hasParentWith(Cuts::abspid == longLivedPid)) return true;
71      }
72      return false;
73    }
74
75    /// @name Histogram
76    Histo1DPtr _h_ppInel;
77
78    /// Cut constants
79    const double ETAMIN = 2.0, ETAMAX = 5.0, PMIN = 2.0*GeV;
80
81  };
82
83
84  RIVET_DECLARE_PLUGIN(LHCB_2018_I1665223);
85
86}