M1 Radiative Transitions in the $B_c$ System after the $B_c^\ast(1S)$ Observation: Radial-Node Cancellation and Quark-Line Filtering

The recent ATLAS observation of the $B_c^*(1S)$ meson fixes the ground-state hyperfine splitting and thereby determines the phase space for $B_c^*(1S)\to B_c(1S)γ$. We study four $1S$ and $2S$ M1 radiative transitions using relativistic Salpeter wave functions calibrated to the measured ground-state