2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/49639We propose the $B_c\to B_u^*γ$ decay as the most suitable probe for the flavour changing neutral transition $c\to uγ$. We estimate the short and long distance contributions to this decay within the standard model and we find them to be comparable; this is in contrast to radiative decays of $D$ mesons, that are completely dominated by the long distance contributions. Since the $c\to uγ$ transition is very sensitive to the physics beyond the standard model, the standard model prediction $Br(B_c\to B_u^*γ)\sim 10^{-8}$ obtained here opens a new window for future experiments. The detection of $B_c\to B_u^*γ$ decay at branching ratio well above $10^{-8}$ would signal new physics.6 pages; presented at Heavy Flavours 8, Southampton, UK, 1999High Energy Physics - Phenomenologytext