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

@misc{wan2026radiative,
  title = {{M1 Radiative Transitions in the $B_c$ System after the $B_c^\ast(1S)$ Observation: Radial-Node Cancellation and Quark-Line Filtering}},
  author = {Bing-Dong Wan},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.00138},
  eprint = {2610.00138},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.00138},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - M1 Radiative Transitions in the B_c System after the B_c^∗(1S) Observation: Radial-Node Cancellation and Quark-Line Filtering
AU  - Bing-Dong Wan
PY  - 2026
DA  - 2026/10/01
PB  - arXiv
DO  - 10.48550/arxiv.2610.00138
UR  - https://arxiv.org/abs/2610.00138
AB  - 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)→ B_c(1S)γ. We study four 1S and 2S M1 radiative transitions using relativistic Salpeter wave functions calibrated to the measured ground-state masses, obtaining Γ[B_c^*(1S)→ B_c(1S)γ]=5.24×10^−2~keV. The allowed transitions show no radial cancellation, whereas the hindered 2S→1S amplitudes are residuals of an approximately twenty-fold cancellation across the radial node. A quark-line-resolved analysis shows a strong asymmetry in the crossed hindered channel: the b-emission contribution undergoes an 𝒪(10^2) internal cancellation while the c̅ contribution remains at 𝒪(20). The corresponding unsigned line strengths show that the small b-current is generated by enhanced cancellation rather than by a smaller unsigned contribution. The unmeasured B_c^*(2S) mass remains the main limitation on the 2S→2S radiative width.
ER  -