Search for Axionlike Particles Produced in e^{+}e^{-} Collisions at Belle II

Area of Science:

• Particle Physics
• High-Energy Physics
• Beyond Standard Model Physics

Background:

• Axionlike particles (ALPs) are hypothetical light pseudoscalar particles.
• ALPs are predicted by extensions of the Standard Model, interacting with gauge bosons.
• Searches for ALPs probe fundamental physics beyond established theories.

Purpose of the Study:

• To search for the direct production of light pseudoscalar particles (ALPs) decaying into two photons.
• To investigate the process e^{+}e^{-}→γa, a→γγ at the Belle II detector.
• To set limits on the coupling strength of ALPs to photons.

Main Methods:

• Utilized data from the Belle II detector at the SuperKEKB collider.
• Analyzed electron-positron collision data corresponding to an integrated luminosity of (445±3) pb^{-1}.
• Searched for a→γγ decays within the mass range 0.2

Main Results:

• No significant evidence for the direct production of ALPs was observed.
• Set 95% confidence level upper limits on the ALP-photon coupling strength (g_{aγγ}) at the level of 10^{-3} GeV^{-1}.
• Established the most restrictive limits to date for ALPs in the mass range 0.2

Conclusions:

• The search places stringent constraints on the existence of light ALPs in the studied mass range.
• The results contribute to narrowing the parameter space for ALPs and theories beyond the Standard Model.
• Future searches with increased luminosity at Belle II can further probe ALP properties.