Search for baryon and lepton number violation in $J/\psi \to {\mathrm{\Lambda }}_c^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.$

Using $1.31\times 10^9$ $J/\psi$ events collected by the BESIII detector at the Beijing Electron Positron Collider, we search for the process $J/\psi \to {\mathrm{\Lambda }}_c^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.$ for the first time. In this process, both baryon and lepton number conservation is violated. No signal is found and the upper limit on the branching fraction $\mathcal{B}(J/\psi \to {\mathrm{\Lambda }}_c^{+}{e}^{-}+\mathrm{c}.\mathrm{c}.)$ is set to be $6.9\times 10^{-8}$ at the 90% confidence level.

Figure 1

Decay diagrams for $J/\psi \to {\mathrm{\Lambda }}_c^{+}{e}^{-}$, where $X$ and $Y$ are leptoquarks, which carry color charge, fractional electric charge, and both lepton and baryon quantum numbers [14].

Figure 2

Distributions of $M_{p{K}^{-}{\pi }^{+}}$ for the $J/\psi \to {\mathrm{\Lambda }}_c^{+}{e}^{-}$ candidate events for signal MC simulation (shaded histogram) and data (dots with error bars), where the signal MC sample is normalized arbitrarily. The inset plot shows a narrow mass range within $(2.23,2.33)\mathrm{GeV}/c^2$, where the arrows represent the signal mass window.