2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/44587The three-body decay $B^0(B_s)\to γν\barν$ can occur via penguin and box diagrams in the standard model (SM). These channels are useful to determine the decay constants $f_B$ ($f_{B_s}$) and $B$ ($B_s$) meson wave function. Using the B meson wave function determined in hadronic $B (B_s)$ decays, we calculate and get the branching ratio of order $10^{-9}$ and $10^{-8}$ for $B^0$ and $B_s$ decay, respectively. They agree with previous calculations.Latex, 9 pages, including 4 figuresHigh Energy Physics - Phenomenologytext