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

TL;DR

This study searches for the rare decay $B^0 o au^+ u_ au o au^- o ext{hadrons}$ using Belle data, setting an upper limit on its branching fraction due to no significant signal detection.

Contribution

First search for $B^0 o au^+ u_ au$ with hadronic tagging at Belle, providing the most stringent upper limit to date.

Findings

No significant signal observed.

Upper limit on branching fraction: $2.5 imes 10^{-4}$.

Data consistent with Standard Model expectations.

Abstract

We search for the process $B^0 \to \pi^- \tau^+ \nu_\tau$ using the full Belle data set of $711\,{\rm fb}^{-1}$, corresponding to $772 \times 10^6 B\bar{B}$ 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 $B^0 \to \pi^- \tau^+ \nu_\tau$ process in the remainder of the event. No significant signal is observed and an upper limit of $\mathcal{B}(B^0 \to \pi^- \tau^+ \nu_\tau) < 2.5 \times 10^{-4}$ is obtained at the $90\%$ confidence level.