Search for $\overline{\Lambda }\text{−}\Lambda $ Baryon-Number-Violating Oscillations in the Decay $J/\psi \to p{K}^{-}\overline{\Lambda }+c.c.$

We report on the first search for $\overline{\Lambda }\text{−}\Lambda $ oscillations in the decay $J/\psi \to p{K}^{-}\overline{\Lambda }+c.c.$ by analyzing $1.31×{10}^{9}\text{}\text{}J/\psi $ events accumulated with the BESIII detector at the BEPCII collider. The $J/\psi $ events are produced using ${e}^{+}{e}^{-}$ collisions at a center of mass energy $\sqrt{s}=3.097\text{}\text{}\mathrm{GeV}$. No evidence for hyperon oscillations is observed. The upper limit for the oscillation rate of $\overline{\Lambda }$ to $\Lambda $ hyperons is determined to be $P\left(\Lambda \right)=\left[B\left(J/\psi \to p{K}^{-}\Lambda +c.c.\right)/B\left(J/\psi \to p{K}^{-}\overline{\Lambda }+c.c.\right)\right]<4.4×{10}^{-6}$ corresponding to an oscillation parameter $\delta {m}_{\Lambda \overline{\Lambda }}$ of less than $3.8×{10}^{-18}\text{}\text{}\mathrm{GeV}$ at the 90% confidence level.