Search for the lepton number violation decay $ω\to π^+ π^+ e^-e^- +c.c.$

TL;DR

This study searches for lepton-number-violating decay $\omega \to \pi^+\pi^+ e^- e^- + c.c.$ via $J/\psi \to \omega \eta$ using the BESIII data set of $N_{J/\psi}=(1.0087 \pm 0.0044) \times 10^{10}$ events. By normalizing to the reference decay $\omega \to \pi^+\pi^-\pi^0$ and employing 5C and 4C kinematic fits plus a 2D fit to invariant masses, the analysis achieves an upper limit on the branching fraction of $\mathcal{B}(\omega \to \pi^+\pi^+ e^- e^- + c.c.) < 2.8 \times 10^{-6}$ at 90% C.L. with no signal observed. The result provides the first experimental constraint on the LNV decay of the $\omega$ meson and contributes to the broader program of testing Majorana neutrino scenarios and beyond-SM physics. The approach demonstrates how large $J/\psi$ datasets can constrain rare LNV processes in light hadrons.

Abstract

The lepton number violation decay $ω\to π^+ π^+ e^-e^- +c.c.$ is searched for via $J/ψ\to ωη$ using a data sample of $(1.0087 \pm 0.0044) \times 10^{10}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider. No significant signal is observed, and the upper limit on the branching fraction of $ω\to π^+ π^+ e^-e^- +c.c.$ at the 90\% confidence level is determined for the first time to be $2.8 \times 10^{-6}$.

Figures (3)

• Figure 1: A possible Feynman diagram for $\omega \to \pi^{+} \pi^{+} e^{-} e^{-}$.
• Figure 2: The projections of the 2D fit of the (a) $M_{3\pi}$ and (b) $M_{\gamma\gamma}$ distributions, where the total PDF is shown by a blue solid curve. The signal PDF is shown by a red solid curve and labeled by $\omega - \eta$. The non-peaking background distribution is shown by a cyan solid curve and labeled by non-$\omega$ -- non-$\eta$. The peaking background in $M_{3\pi}$ is shown by a pink solid curve and labeled by $\omega$ -- non-$\eta$. The peaking background in $M_{\gamma\gamma}$ is shown by a green solid line and labeled by non-$\omega$ -- $\eta$.
• Figure 3: The 2D distribution of $M_{\gamma\gamma}$ versus $M_{\pi^+ \pi^+ e^-e^-}$ of the candidate events from the $J/\psi$ data, where the red box shows the signal region.