Laura Zani

02 May 2023

Abstract: The possibility of dark sectors weakly coupling to Standard Model (SM) particles through new light mediators is explored at the Belle II experiment. We present here results from three different searches, for a long-lived (pseudo)scalar particle; for a di-tau resonance in four-muon final states events and the update on the search for a Z′ boson decaying invisibly in events with two muons plus missing energy, performed on samples from the data collected by the Belle II detector during 2019-2021 data taking. We report the search for τ → ℓα decays, with α a new invisible boson, and the first successful untagged reconstruction of tau pairs events searching for the neutrinoless decays τ → ℓφ. Finally, we present the world’s most precise measurement of the τ lepton mass.

Keyword(s): Moriond QCD23