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

We report on the first search for $\overline{\mathrm{\Lambda }}\text{−}\mathrm{\Lambda }$ oscillations in the decay $J/\psi \to p{K}^{-}\overline{\mathrm{\Lambda }}+\mathrm{c}.\mathrm{c}.$ by analyzing $1.31\times {10}^{9}J/\psi$ 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 $\sqrt{s}=3.097\mathrm{GeV}$. No evidence for hyperon oscillations is observed. The upper limit for the oscillation rate of $\overline{\mathrm{\Lambda }}$ to $\mathrm{\Lambda }$ hyperons is determined to be $\mathcal{P}(\mathrm{\Lambda })=[\mathcal{B}(J/\psi \to p{K}^{-}\mathrm{\Lambda }+\mathrm{c}.\mathrm{c}.)/\mathcal{B}(J/\psi \to p{K}^{-}\overline{\mathrm{\Lambda }}+\mathrm{c}.\mathrm{c}.)]<4.4\times {10}^{-6}$ corresponding to an oscillation parameter $\delta m_{\mathrm{\Lambda }\overline{\mathrm{\Lambda }}}$ of less than $3.8\times {10}^{-18}\mathrm{GeV}$ at the 90% confidence level.

Figure 1

Distribution of $M_{p{\pi }^{-}}$ for (a) WS events in the signal region and (inset) over the full span, where the filled circle with the error bar is from data, the pink filled histogram, normalized arbitrarily, stems from simulated WS signal events, and the arrows in the inset figure show the edges of the signal region; (b) RS events from data, where the filled circles with error bars are from data, the blue solid line represents the result of the fit, and the dashed line shows the background contribution.