Speaker
Description
We present a search for the yet-unobserved $B \rightarrow D^{(*)}\eta\pi$ decay at Belle and Belle II. This search aims to provide insights into the semi-leptonic (SL) gap, which refers to the deficit in the sum of the branching fractions of known exclusive decays compared to the measured inclusive $b \rightarrow c\ell\nu$ branching fraction. Common models addressing this deficit suggest the existence of $B \rightarrow D^{(*)}\eta\ell\nu$ decays with a branching fraction of the order of $10^{-3}$, which could imply a branching fraction of $B \rightarrow D^{(*)}\eta\pi$ of the order of $10^{-4}$ based on a naive prediction derived from the ratio of branching fractions of $B \rightarrow D^{(*)}\pi$ and $B \rightarrow D^{(*)}\ell\nu$. The study of $B \rightarrow D\eta\pi$ will also aid in understanding the two pole structure of $D^{*}_{0}(2400)$ meson through the coupled channel $D\eta$. Utilizing the ~1.1 ab$^{-1}$ of data collected at Belle and Belle II combined, we are initiating a preliminary search to investigate and potentially observe these decays for the first time. This search is also expected to significantly enhance our understanding of the $B$ hadronic sector.
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