We search for the tree-diagram dominated process $B^+ \rightarrow p \overline{n} \pi^0$, using a data sample of $772 \times 10^6~B\overline B$ pairs collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. This is the first search with the Belle detector for a decay mode including an anti-neutron. No significant signal is observed and an $90\%$ credible upper limit on the branching fraction is set at $6.1\times10^{-6}$.
Comment: 5 pages, 2 figures, 1 table. To be submitted to PRD. arXiv admin note: text overlap with arXiv:1912.05999