Search for lepton-number- and baryon-number-violating tau decays at Belle

Abstract

We search for lepton-number- and baryon-number-violating decays tau(-) -> (p) over bare(+)e(-), (p) over bare(-)e(-), (p) over bare(+)mu(-), (p) over bare(-)mu(+), (p) over bar mu(+)mu(-), and (p) over bar mu(-)mu(-) using 921 fb(-1) of data, equivalent to (841 +/- 12) x 10(6) tau(+)tau(-) events, recorded with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. In the absence of a signal, 90% confidence-level upper limits are set on the branching fractions of these decays in the range (1.8 - 4.0) x 10(-8). We set the world's first limits on the first four channels and improve the existing limits by an order of magnitude for the last two channels.