Measurement of the forward η meson production rate in p-p collisions at √s=13 TeV with the LHCf-Arm2 detector

The forward eta mesons production has been observed by the Large Hadron Collider forward (LHCf) experiment in proton-proton collision at root s = 13 TeV. This paper presents the measurement of the inclusive production rate of eta in pT< 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's atmosphere by ultra-energetic cosmic rays.