Probing charged lepton flavor violation with axion-like particles at Belle II

Understand

We study charged lepton flavor violation associated with a light leptophilic axion-like particle (ALP), $X$, at the $B$-factory experiment Belle II.

• We focus on production of the ALP in the tau decays $\tau \to X l$ with $l=e,\mu$, followed by its decay via $X\to l^- l^+$.
• The ALP can be either promptly decaying or long-lived.
• We perform Monte-Carlo simulations, recasting a prompt search at Belle for lepton-flavor-violating $\tau$ decays, and propose a displaced-vertex (DV) search.