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ATLAS_2011_I894867

Measurement of the inelastic proton-proton cross-section at $\sqrt{s} = $7 TeV.
Experiment: ATLAS (LHC)
Inspire ID: 894867
Status: VALIDATED
Authors:
  • Anton Karneyeu
  • Sercan Sen
References: Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Inelastic events (non-diffractive and inelastic diffractive).

Inelastic cross-section is measured for $\xi > 5 \times 10^{-6}$, 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_2011_I894867.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"

namespace Rivet {


  class ATLAS_2011_I894867 : public Analysis {
  public:

    DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2011_I894867);

    void init() {
      declare(FinalState(), "FS");
      _h_sigma = bookHisto1D(1, 1, 1);
    }


    void analyze(const Event& event) {

      const FinalState& fs = apply<FinalState>(event, "FS");
      if (fs.size() < 2) vetoEvent; // need at least two particles to calculate gaps

      const Particles particles = fs.particles(cmpMomByEta);
      double etaprev = particles.front().eta();
      double gapcenter = etaprev;
      double detamax = -1;
      for (const Particle& p : particles) { // sorted from minus to plus
        const double deta = p.eta() - etaprev; // guaranteed positive
        if (deta > detamax) { // largest gap so far
          detamax = deta;
          gapcenter = (p.eta() + etaprev)/2.; // find the center of the gap to separate the X and Y systems.
        }
        etaprev = p.eta();
      }

      FourMomentum mxFourVector, myFourVector;
      for (const Particle& p : particles)
        (p.eta() > gapcenter ? mxFourVector : myFourVector) += p.momentum();
      const double m2 = max(mxFourVector.mass2(), myFourVector.mass2());
      const double xi = m2/sqr(sqrtS()); // sqrt(s) = 7000 GeV
      if (xi < 5e-6) vetoEvent;

      _h_sigma->fill(sqrtS()/GeV, event.weight());
    }


    void finalize() {
      scale(_h_sigma, crossSection()/millibarn/sumOfWeights());
    }


    Histo1DPtr _h_sigma;

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2011_I894867);

}