RHICf -- Measurements of very forward particles at RHIC

In this presentation, we will introduce a newly proposed experiment at Relativistic Heavy Ion Collider (RHIC), named as RHICf (RHIC-forward). The proposal is to install a high-resolution electromagnetic calorimeter in front of a zero-degree hadron calorimeter (ZDC) at the PHENIX interaction point, and to measure cross sections and single spin asymmetries of very forward ($\eta > 6$) neutral particles in proton-proton collision at $\sqrt{s}=510$ GeV. Such information helps to understand the production mechanism, which is beyond purturbative QCD. In addition, together with measurements at LHC, these data are invaluable for calibrating ultra-high energy cosmic ray measurements.