Rivet analyses

title: 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: - Expt page: ATLAS-STDM-2010-11 - arXiv: 1104.0326

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

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

class ATLAS_2011_I894867 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2011_I894867);

void init() {
  declare(FinalState(), "FS");
  book(_h_sigma, 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);
}


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


Histo1DPtr _h_sigma;

};

RIVET_DECLARE_PLUGIN(ATLAS_2011_I894867);

} ```