Search for the lepton number violating process $J/ψ\to K^+K^+e^-e^- +c.c.$

TL;DR

This work reports the first search for a lepton-number-violating decay of the J/ψ meson, J/ψ → K^+K^+e^-e^- + c.c., using a dataset of (10087±44)×10^6 J/ψ events collected with BESIII. Employing a blinded analysis, stringent track/PID criteria, and a 4C kinematic fit, the study finds one event in the signal region with negligible background, yielding a branching-fraction upper limit of ≤ 2.1×10^-9 at 90% CL and providing Majorana-mass dependent upper limits across m_{ν_M} from 0.575 to 1.525 GeV/c^2. These results constrain LNV processes and offer inputs for models involving Majorana neutrinos, translating into limits on the mixing parameter |V_{eν_M}|^2 in the explored mass range. The analysis demonstrates the capability of BESIII to probe rare LNV decays in the charmonium system and sets a benchmark for future searches.

Abstract

Based on $(10087\pm 44)\times10^{6}$ $J/ψ$ events collected with the BESIII detector, we search for the lepton number violating decay $J/ψ\to K^+K^+e^-e^- + c.c.$ for the first time. The upper limit on the branching fraction of this decay is set to be $2.1 \times 10^{-9}$ at the 90$\%$ confidence level with a frequentist method. This is the first search for $J/ψ$ decays with the lepton number change by two, offering valuable insights into the underlying physical processes.

Figures (3)

• Figure 1: Possible Feynman diagrams of $J/\psi \to K^{+}K^{+}e^{-}e^{-}+c.c$.
• Figure 2: The distribution of $M_{K^{+}K^{+}e^{-}e^{-}+c.c.}$, where the blue histogram represents the simulated shape of signal, the yellow filled histogram represents data, and the red arrows indicate the signal region.
• Figure 3: The ULs at the 90% CL for the data sample as a function of $m_{\nu_M}$ for the decay $J/\psi \to 2\nu_M\ (\to K^+e^-)$.