Search for the decay B → D*ηπ in Belle II

We present a search for the yet-unobserved B → D*ηπ decay at Belle II. This search can provide information for the understanding of the so-called semileptonic gap, which is the deficit in the sum of the branching fractions (BF) of known exclusive decays with respect to the measured inclusive 𝑏 → 𝑐ℓ𝜈 branching fraction. Widely used models to fill this deficit assume the existence of B → D*ηπ decays with BF of 4 × 10−3 , which could imply a BF of B → D*ηπ of about 2 × 10−4 . Using the full sample collected by the Belle II experiment in 2019-2022, the expected upper limit on the BF of B → D*ηπ is 1 × 10−4 . This search would also improve knowledge of the B hadronic sector significantly.