Search for $B^0 to pi^- tau^+ u_tau$ with hadronic tagging at Belle

We search for the process $B^0 to pi^- tau^+ u_tau$ using the full Belle data set of $711,{rm fb}^{-1}$, corresponding to $772 times 10^6 Bbar{B}$ pairs, collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We reconstruct one $B$ meson in a hadronic decay and search for the $B^0 to pi^- tau^+ u_tau$ process in the remainder of the event. No significant signal is observed and an upper limit of $mathcal{B}(B^0 to pi^- tau^+ u_tau) < 2.5 times 10^{-4}$ is obtained at the $90%$ confidence level.