Search for Sub-GeV Invisible Particles in Inclusive Decays of J/ψ to ϕ

Area of Science:

• Particle Physics
• High Energy Physics
• Experimental Physics

Background:

• Searches for new physics beyond the Standard Model often involve looking for invisible particles.
• The J/ψ meson is a well-studied system in particle physics, providing a rich source of data for decay studies.

Purpose of the Study:

• To search for an invisible particle (X) with a mass between 0 and 0.96 GeV/c² in the J/ψ→ϕ+X decay process.
• To set upper limits on the branching fractions of J/ψ→ϕ+X and η→invisible decays.
• To establish a new method for searching for sub-GeV invisible particles.

Main Methods:

• Utilized a large dataset of J/ψ events collected by the BESIII detector.
• Fully reconstructed the ϕ meson and applied efficient vetoes for photons and hadrons.
• Determined the recoil mass against the ϕ meson using kinematic constraints.

Main Results:

• No significant signal for an invisible particle X was observed in the J/ψ→ϕ+X decay.
• An upper limit of 7.0×10⁻⁸ (90% confidence level) was set for the inclusive branching fraction of J/ψ→ϕ+X.
• Upper limits for the branching fraction of η→invisible were improved by over 4 times, reaching 2.4×10⁻⁵ (90% confidence level).

Conclusions:

• The study provides stringent constraints on the existence of sub-GeV invisible particles.
• The developed analysis technique offers a promising avenue for future searches for invisible particles in other decays and experiments.
• The results contribute to the ongoing quest for new physics phenomena.