Speaker
Description
We report a search for a heavy neutral lepton (HNL) that mixes
predominantly with ντ . The search utilizes data collected with the
Belle detector at the KEKB asymmetric energy e+e− collider. The data
sample was collected at and just below the center-of-mass energies of the
Υ(4S) and Υ (5S) resonances and has an integrated luminosity of 915 fb−1,
corresponding to (836 ± 12) × 106 e+e− → τ+τ− events. We search for the
production of the HNL (denoted N) in the decay τ− → π−N followed by its
decay via N → μ+μ−ντ. The search focuses on the parameter-space region
in which the HNL is long-lived so that the μ+μ− originate from a common
vertex that is significantly displaced from the collision point of the
KEKB
beams. Consistent with the expected background yield, one event is
observed
in the data sample after the application of all the event-selection
criteria. We report limits on the mixing parameter of the HNL with
the τ neutrino
as a function of the HNL mass.
