Signal extraction in the analysis of $\omega$ and $\phi$ meson production at forward rapidity in pp collisions at the LHC

This note contains details on the technique used for the signal extraction in the low-mass dimuon analyses in the rapidity range $2.5<y<4$, with particular attention for the $\omega$ and $\phi$ mesons. The main sources contributing to low mass region (LMR) are the light meson decays into muon pairs, the so-called hadronic cocktail, and a contribution coming from semimuonic decays of charm and beauty hadrons (referred in the following as open charm/beauty processes). Due to the unsatisfactory description of the continuum based on the open charm and beauty, these contributions are replaced with an empirical continuum which is fitted to the data after the subtraction of the hadronic cocktail.