Search for the baryon number and lepton number violating decays τ⁻→ Λπ⁻ and τ⁻→ Λ̄π⁻ at Belle II

We present a search for the baryon number B and lepton number L violating decays τ⁻ → Λ π⁻ and τ⁻ → Λ̄ π⁻ produced from the e⁺e⁻→ τ⁺τ⁻ process, using a 364 fb⁻¹ data sample collected by the Belle~II experiment at the SuperKEKB collider. No evidence of signal is found in either decay mode, which have |Δ(B-L)| equal to $2$ and $0$, respectively. Upper limits at 90% credibility level on the branching fractions of τ⁻ → Λπ⁻ and τ⁻ → Λ̄π⁻ are determined to be 4.7 × 10⁻⁸ and 4.3 × 10⁻⁸, respectively.