Measurements of electroweak penguin and lepton-flavour violating BB decays to final states with missing energy at Belle and Belle ~II

Collaboration
for the collaboration.
Dec 17, 2024
6 pages
Published in:
  • PoS ICHEP2024 (2025) 418
Contribution to:
  • Published: Dec 17, 2024
Experiments:

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Abstract: (SISSA)
Electroweak penguin and lepton-flavour violating BB decays are key focuses of the Belle II physics program. These processes are particularly challenging due to the presence of neutrinos in the final states, resulting in `missing energy' in the rare bsb\to s transitions. Using electron-positron collision data collected at the Υ(4S)\Upsilon(4S) resonance, we present the first evidence for B+K+ννˉB^+\to K^+\nu\bar{\nu} decay and the most stringent upper limit on B0K0τ+τB^0\to K^{*0}\tau^+\tau^- decay. Additionally, combining Belle and Belle II data, we report the first search on lepton-flavour violating B0KS0τ±B^0\to K^{0}_S\tau^\pm\ell^\mp (=e,μ\ell=e,\mu) decays.