Belle II Collaboration

13 April 2021

Abstract: This note describes the rediscovery of B → η' K decays in Belle II data, both in the charged and neutral final state: B0 → η' KS and B± → η' K± . The η' is searched for in two decay modes: η' → ηπ+ π− with η → γγ, and η' → ργ. The analysis uses data collected in 2019 and 2020 at the SuperKEKB asymmetric e+ e− collider, with an integrated luminosity of 62.8 fb−1 , corresponding to 68.2 million of BB pairs produced. The signal yield is obtained via an unbinned maximum likelihood fit to signal sensitive variables, obtaining branching ratios: BR( B± → η' K±) = 63.4 (+3.4/−3.3) (stat) ± 3.2 (syst) × 10-6 BR( B0 → η' K ) = 59.9 (+5.8/-5.5) (stat) ± 2.9 (syst) × 10-6 which are consistent with world average.

Keyword(s): b->qqs ; charmless b decay ; TDCPV