Rivet analyses

title: LHCF_2023_I2658888

Measurement of the forward $\eta$ meson production rate in p-p collisions at $\sqrt{s} = 13$~TeV with the LHCf-Arm2 detector

Experiment: LHCF (LHC)

Inspire ID: 2658888

Status: VALIDATED

Authors: - Eugenio Berti - LHCf collaboration

References: - JHEP 10 (2023) 169 - DOI:10.1007/JHEP10(2023)169 - arXiv: 2305.06633

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - Measurement of the inclusive $\eta$ meson production rate at $p_{T} < 1.10 GeV/c$ in $\sqrt{s} = 13$~TeV proton-proton collisions, expressed as a function of the Feynman variable $\x_{F} = 2 p_{Z}/sqrt(s)$.

The forward $\eta$ mesons production has been observed by the Large Hadron Collider forward (LHCf) experiment in proton-proton collision at $\sqrt{s}$ = 13 TeV. This paper presents the measurement of the inclusive production rate of $\eta$ in $p_T<$ 1.1 GeV/c, expressed as a function of the Feynman-x variable. These results are compared with the predictions of several hadronic interaction models commonly used for the modelling of the air showers produced by ultra-high energy cosmic rays. This is both the first measurement of $\eta$ mesons from LHCf and the first time a particle containing strange quarks has been observed in the forward region for high-energy collisions. These results will provide a powerful constraint on hadronic interaction models for the purpose of improving the understanding of the processes underlying the air showers produced in the Earth atmosphere by ultra-energetic cosmic rays.

Source code:LHCF_2023_I2658888.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Measurement of forward neutron(+ antineutron) production in proton-proton Collisions at 13 TeV class LHCF_2023_I2658888 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCF_2023_I2658888);

/// @name Analysis methods
//@{

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  declare(UnstableFinalState(), "UFS");

  // Book histograms
  book(_h_eta_xf, 1, 1, 1);
}

/// Perform the per-event analysis
void analyze(const Event& event) {

  const UnstableFinalState& ufs = apply<UnstableFinalState>(event, "UFS");

  for (const Particle& p : ufs.particles()) {
    // select eta meson
    if (p.abspid() != PID::ETA) continue;
    // select pt range
    const double pt = abs(p.pT() / GeV);
    if (pt >= 1.10) continue; // fill considering both LHCf (Arm1 and Arm2) sides
    // compute xf variable
    const double pz = abs(p.pz() / GeV);
    const double ss = sqrtS() / GeV;
    const double xf = 2. * pz / ss;

    _h_eta_xf->fill(xf, xf);
  }
}

/// Normalise histograms etc., after the run
void finalize() {

  const double sumWeights = 2. * sumOfWeights(); // scale considering the LHCf Arm2 side alone

  scale(_h_eta_xf, 1. / (sumWeights)); // scale to production rate
}
//@}

private:

/// @name Histograms
//@{
Histo1DPtr _h_eta_xf;
//@}

};

// The hook for the plugin system RIVET_DECLARE_PLUGIN(LHCF_2023_I2658888);

} ```