The LHC-forward experiment (LHCf), located at the Large Hadron Collider (LHC), is designed to
measure the production cross section of neutral particles in the very-forward region, covering the
pseudorapidity region above 8.4 (up to zero-degree particles). By measuring the very-forward
particle production rates at the highest energy possible at an accelerator, LHCf will provide
fundamental informations to improve phenomenological hadronic interaction models used in the
simulation of air-showers induced by ultra-high-energy cosmic rays in the atmosphere. The
experiment consists of two small independent detectors placed 140 metres away from the ATLAS
interaction point (IP1), on opposite sides. Each detector is made of two sampling and position
sensitive calorimeters.
This contribution will focus on the Run II physics results of LHCf in proton-proton collisions at 13
TeV. At first the photon energy spectrum will be presented and compared with the predictions of
several hadronic interaction models. The advantages of the ATLAS-LHCf combined analysis will
then be discussed and the preliminary spectrum of very-forward photons produced in diffractive
collisions (tagged by ATLAS) will be shown together with models predictions. The preliminary
Feynman-x and transverse momentum spectrum of $\pi^0$, and the Feynman-x spectrum of $\eta$ will also
be presented. Photons and $\pi^0$ production cross section provides important information about the
electromagnetic component of an air-shower, while $\eta$ measurements give the possibility to probe
the strange-quark related contribution. Finally, the neutron energy spectrum measured in several
pseudorapidity regions will be shown and compared with the predictions of various hadronic
interaction models. From these measurements the average inelasticity of the collisions, which
strongly affects the development of an air-shower, has also been extracted.