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ATLAS_2016_I1468167

Measurement of the inelastic proton--proton cross-section at $\sqrt{s} = 13\,\text{TeV}$
Experiment: ATLAS (LHC)
Inspire ID: 1468167
Status: VALIDATED
Authors:
  • Zachary Marshall
  • Christian Gutschow
References: Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • Inelastic events (non-diffractive and inelastic diffractive).

Inelastic cross-section is measured for $\xi > 1 \times 10^{-6}$, where $\xi=M_X^2/s$ is calculated from the invariant mass, $M_X$, of hadrons selected using the largest rapidity gap in the event.

Source code: ATLAS_2016_I1468167.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// Measurement of the inelastic proton-proton cross-section at \sqrt{s} = 13 TeV
 9  class ATLAS_2016_I1468167 : public Analysis {
10  public:
11
12
13    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2016_I1468167);
14
15
16    /// Initialisation
17    void init() {
18      declare(FinalState(), "FS");
19      book(_h_sigma, 1, 1, 1);
20    }
21
22
23    /// Per-event analysis
24    void analyze(const Event& event) {
25
26      // Get all particles, sorted from minus to plus in eta
27      const FinalState& fs = apply<FinalState>(event, "FS");
28      if (fs.size() < 2) vetoEvent; // need at least two particles to calculate gaps
29      const Particles particles = fs.particles(cmpMomByEta);
30
31      // Find this event's largest gap size and center
32      double etapre = particles.front().eta();
33      double gapcenter = 0.;
34      double gapsize = -1;
35      for (const Particle& p : particles) {
36        const double gap = fabs(p.eta() - etapre);
37        if (gap > gapsize) { // new largest gap
38          gapsize = gap;
39          gapcenter = (p.eta() + etapre)/2.;
40        }
41        etapre = p.eta();
42      }
43
44      // Calculate xi variable of the more massive side of the event, and apply xi cut
45      FourMomentum mxFourVector, myFourVector;
46      for (const Particle& p : particles) {
47        ((p.eta() > gapcenter) ? mxFourVector : myFourVector) += p;
48      }
49      const double M2 = max(mxFourVector.mass2(), myFourVector.mass2());
50      const double xi = M2/sqr(sqrtS()); // sqrt(s)=7000 GeV, note that units cancel
51      if (xi < 1e-6) vetoEvent;
52
53      // Fill the histogram
54      _h_sigma->fill(sqrtS()/GeV);
55    }
56
57
58    /// Scale the acceptance histogram to inelastic cross-section
59    void finalize() {
60      scale(_h_sigma, crossSection()/millibarn/sumOfWeights());
61    }
62
63
64    /// Histogram
65    Histo1DPtr _h_sigma;
66
67  };
68
69
70  // The hook for the plugin system
71  RIVET_DECLARE_PLUGIN(ATLAS_2016_I1468167);
72
73}