Abstract
Using a data sample of $(1310.6 \pm 7.0)\times 10^6$ $J/\psi$ events collected with the BESIII detector operating at the BEPCII collider, we perform the first experimental search for invisible decays of a light vector meson ($V=\omega,\phi$) via $J/\psi \to V \eta$ decays. The decay of $\eta \to \pi^+\pi^-\pi^0$ is utilized to tag the $V$ meson decaying into the invisible final state. No evidence for a significant invisible signal is observed, and the upper limits on the ratio of branching fractions at the 90\% confidence level are determined to be $\frac{\mathcal{B}(\omega \rightarrow \rm{invisible})}{\mathcal{B}(\omega \to \pi^+\pi^-\pi^0)} < 8.1 \times 10^{-5}$ and $\frac{\mathcal{B}(\phi \to \rm{invisible})}{\mathcal{B}(\phi \to K^+K^-)} < 3.4\times 10^{-4}$. By using the world average values of $\mathcal{B}(\omega \to \pi^+\pi^-\pi^0)$ and $\mathcal{B}(\phi\to K^+K^-)$, the upper limits on the decay branching fractions at the $90\%$ confidence level are set as $\mathcal{B}(\omega \to \rm{invisible})< 7.3 \times 10^{-5}$ and $\mathcal{B}(\phi \to \rm{invisible})< 1.7\times 10^{-4}$, respectively.
Highlights
There is strong evidence from many astrophysical observations for the existence of dark matter, its nature is still mysterious
We compute the upper limits on the ratio of branching fractions of the invisible decay to that of the corresponding visible decay, Bðω→invisibleÞ Bðω→π þ π − π 0 Þ
By using the branching fractions of ω → πþπ−π0 and φ → KþK− quoted by the Particle Data Group (PDG) [21], the upper limits on the invisible decay branching fractions at the 90% C.L. are calculated to be Bðω → invisibleÞ < 7.3 ×
Summary
There is strong evidence from many astrophysical observations for the existence of dark matter, its nature is still mysterious. The branching fraction of the invisible decays might be enhanced by several orders of magnitude in the presence of light dark matter (LDM) particles χ [2,3,4] as described in Refs. The experimental exploration of invisible decays for other quarkonium states (qq , q 1⁄4 u, d or s) may help to constrain the masses of the LDM particles and the coupling of the U boson to light quarks [15,16]. The branching fraction BðV → χχÞ (V 1⁄4 ω, φ) is predicted to be up to the level of 10−8 by assuming the same cross section for the time reversed processes, σðqq → χχÞ≃ σð χχ → qq Þ [6]. We report the first experimental search for the invisible decays of ω and φ mesons via J=ψ → Vη using ð1310.6 Æ 7.0Þ × 106 J=ψ events collected with the BESIII detector in 2009 and 2012 [17]
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