We report a search for a heavy neutral lepton (HNL) that mixes predominantly with. The search utilizes data collected with the Belle detector at the KEKB asymmetric energycollider. The data sample was collected at and just below the center-of-mass energies of theandresonances and has an integrated luminosity of, corresponding toevents. We search for production of the HNL (denoted) in the decayfollowed by its decay via. The search focuses on the parameter-space region in which the HNL is long-lived, so that theoriginate 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 application of all the event-selection criteria. We report limits on the mixing parameter of the HNL with theneutrino as a function of the HNL mass.
Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to non-federal websites. Their policies may differ from this site.
-
Published by the American Physical Society 2024 Free, publicly-accessible full text available June 1, 2025 -
Free, publicly-accessible full text available March 1, 2025
-
Free, publicly-accessible full text available February 1, 2025
-
Free, publicly-accessible full text available February 1, 2025
-
A bstract We report a search for the charged-lepton flavor violation in Υ(2
S ) →ℓ ∓τ ± (ℓ =e, μ ) decays using a 25 fb− 1Υ(2S ) sample collected by the Belle detector at the KEKBe +e − asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions ( ) at 90% confidence level. We obtain the most stringent upper limits:$$ \mathcal{B} $$ (Υ(2$$ \mathcal{B} $$ S )→ μ ∓τ ± )< 0. 23× 10− 6and (Υ(2$$ \mathcal{B} $$ S )→ e ∓τ ± )< 1. 12× 10− 6.Free, publicly-accessible full text available February 1, 2025 -
We measure the branching fraction of the decayusing data collected with the Belle II detector. The data contain 387 millionpairs produced incollisions at theresonance. We reconstructdecays from an analysis of the distributions of theenergy and thehelicity angle. We determine the branching fraction to be, in agreement with previous results. Our measurement improves the relative precision of the world average by more than a factor of two.
Published by the American Physical Society 2024 Free, publicly-accessible full text available June 1, 2025