Search for B -> tau nu and B -> K nu nubar Decays with a Fully Reconstructed B at Belle

TL;DR

This paper reports a search for rare B meson decays into tau neutrino and K neutrino pairs using the Belle detector, setting upper limits due to no significant signal detection.

Contribution

It introduces a method of fully reconstructing one B meson to improve sensitivity in searching for B -> tau nu and B -> K nu nubar decays.

Findings

No significant evidence for the decays was observed.

Upper limits were set: B(B -> tau nu) < 1.8×10^-4, B(B -> K nu nubar) < 3.6×10^-5.

The analysis demonstrates the effectiveness of the full reconstruction technique.

Abstract

We present a search for the decays B -> tau nu and B -> K nu nubar in a 253 fb^-1 data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy B factory. Combinatorial and continuum backgrounds are suppressed by selecting a sample of events with one fully reconstructed B. The decay products of the B on the other side of the event are analyzed to search for B -> tau nu and B -> K nu nubar decays. We find no significant evidence for a signal and set 90% confidence level upper limits of B(B -> tau nu) < 1.8*10^-4 and B(B -> K nu nubar) < 3.6*10^-5.