Performance studies of LHCf and ATLAS-ZDC for very forward neutron measurement

It is important to understand hadronic interactions for the indirect measurement of high energy cosmic rays that are $E>10^{15}$ eV. Large Hadron Collider forward (LHCf) and ATLAS Zero Degree Calorimeter (ZDC) measure neutral particles generated in the very forward region of pp collisions at LHC. The LHCf detector is a calorimeter that has a thickness of 1.7 interaction lengths, resulting in large hadronic shower particle leakage. To address this, the combined analysis with ATLAS-ZDC which is installed behind the LHCf and has a thickness of 3.4 interaction lengths, enables an improvement in the energy resolution of hadronic particles from 40% to 20%, which was confirmed with 350GeV proton beam at SPS. In 2022, we conducted the LHCf+ATLAS-ZDC joint operation with pp collision at $\sqrt{s}$=13.6TeV. We evaluated the improvement in resolution for very forward neutron measurement using the operational data with joint analysis. Additionally, neutron trigger efficiency and particle identification (PID) efficiency were studied with Monte Carlo simulations.