Rivet analyses

title: ALICE_2012_I1181770

Measurement of inelastic, single- and double-diffraction cross sections in proton--proton collisions at the LHC with ALICE

Experiment: ALICE (LHC)

Inspire ID: 1181770

Status: VALIDATED

Authors: - Martin Poghosyan - Sercan Sen - Burak Bilki - Andy Buckley

References: - arXiv: 1208.4968

Beams: p+ p+

Beam energies: (450.0, 450.0); (1380.0, 1380.0); (3500.0, 3500.0)GeV

Run details: - Inelastic events (non-diffractive and inelastic diffractive).

Measurements of cross-sections of inelastic and diffractive processes in proton-proton collisions at $\sqrt{s} = 900$, 2760 and 7000 GeV. The fractions of diffractive processes in inelastic collisions were determined from a study of gaps in charged particle pseudorapidity distributions. Single-diffractive events are selected with $M_{X} < 200~\GeV/c^2$ and double-diffractive events defined as NSD events with $\Delta\eta > 3$. To measure the inelastic cross-section, beam properties were determined with van der Meer scans using a simulation of diffraction adjusted to data. Note that these are experimental approximations to theoretical concepts -- it is not totally clear whether the data point values are model-independent.

Source code:ALICE_2012_I1181770.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {

class ALICE_2012_I1181770 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(ALICE_2012_I1181770);


void init() {
  // Projection setup
  declare(ChargedFinalState(), "CFS");

  // Book histograms
  book(_h_frac_sd_inel, 1, 1, 1);
  book(_h_frac_dd_inel, 2, 1, 1);
  book(_h_xsec_sd, 3, 1, 1);
  book(_h_xsec_dd, 4, 1, 1);
  book(_h_xsec_inel, 5, 1, 1);
}


void analyze(const Event& event) {
  const ChargedFinalState& cfs = apply<ChargedFinalState>(event, "CFS");
  if (cfs.size() < 2) vetoEvent; // need at least two particles to calculate gaps

  // Fill INEL plots for each event
  _h_xsec_inel->fill(sqrtS() / GeV);

  // Identify particles with most positive/most negative rapidities
  const Particles particlesByRap = cfs.particles(cmpMomByRap);
  const Particle pslowest = particlesByRap.front();
  const Particle pfastest = particlesByRap.back();

  // Find gap sizes
  const Particles particlesByEta = cfs.particles(cmpMomByEta); // sorted from minus to plus
  const size_t num_particles = particlesByEta.size();
  vector<double> gaps;
  for (size_t ip = 1; ip < num_particles; ++ip) {
    const Particle& p1 = particlesByEta[ip - 1];
    const Particle& p2 = particlesByEta[ip];
    const double gap = p2.eta() - p1.eta();
    assert(gap >= 0);
    gaps.push_back(gap);
  }

  // First, last, and largest gaps
  const double gapmax = *max_element(gaps.begin(), gaps.end());
  const double gapbwd = gaps.front();
  const double gapfwd = gaps.back();

  // Mx calculation
  FourMomentum p4lead;
  if (pslowest.pid() == PID::PROTON && pfastest.pid() == PID::PROTON) {
    p4lead = (fabs(pslowest.rapidity()) > fabs(pfastest.rapidity())) ? pslowest.momentum()
                                                                     : pfastest.momentum();
  }
  else if (pslowest.pid() == PID::PROTON) {
    p4lead = pslowest.momentum();
  }
  else if (pfastest.pid() == PID::PROTON) {
    p4lead = pfastest.momentum();
  }
  const double Mx = sqrt((sqrtS() - p4lead.E() - p4lead.p3().mod())
                         * (sqrtS() - p4lead.E() + p4lead.p3().mod()));

  // Fill SD (and escape) if Mx is sufficiently low
  if (Mx < 200 * GeV) {
    _h_xsec_sd->fill(sqrtS() / GeV);
    return;
  }

  // Also remove SD-like events in NSD events
  if (fuzzyEquals(gapbwd, gapmax) || fuzzyEquals(gapfwd, gapmax)) vetoEvent;

  // Fill DD plots
  if (gapmax > 3) _h_xsec_dd->fill(sqrtS() / GeV);
}


void finalize() {

  // get the ratio plots: SD/inel, DD/inel
  divide(_h_xsec_sd, _h_xsec_inel, _h_frac_sd_inel);
  divide(_h_xsec_sd, _h_xsec_inel, _h_frac_dd_inel);

  const double scaling = crossSection() / millibarn / sumOfWeights();
  scale(_h_xsec_sd, scaling);
  scale(_h_xsec_dd, scaling);
  scale(_h_xsec_inel, scaling);
}

private:

Estimate1DPtr _h_frac_sd_inel;
Estimate1DPtr _h_frac_dd_inel;
Histo1DPtr _h_xsec_sd;
Histo1DPtr _h_xsec_dd;
Histo1DPtr _h_xsec_inel;

};

RIVET_DECLARE_PLUGIN(ALICE_2012_I1181770);

} ```