Search for Rare b→dℓ^{+}ℓ^{-} Transitions at Belle.

Area of Science:

• Particle Physics
• High-Energy Physics
• Rare B Decays

Background:

• Flavor-changing neutral-current (FCNC) decays are rare processes predicted by the Standard Model.
• Searching for these decays, such as b→dℓ⁺ℓ⁻, provides a sensitive probe of new physics beyond the Standard Model.
• Previous searches have constrained branching fractions, but new data allows for improved sensitivity.

Purpose of the Study:

• To search for the FCNC rare decays B⁺,⁰→(η,ω,π⁺,⁰,ρ⁺,⁰)e⁺e⁻ and B⁺,⁰→(η,ω,π⁰,ρ⁺)μ⁺μ⁻.
• To set new world-leading upper limits on the branching fractions for these decay channels.
• To explore previously unsearched decay modes involving ω and ρ mesons.

Main Methods:

• Analysis of a large dataset of 772×10⁶ BB̄ events collected by the Belle detector at the KEKB asymmetric-energy e⁺e⁻ collider.
• Data collected at the ϒ(4S) resonance.
• Event reconstruction and selection for specific B meson decay modes into leptons (e⁺e⁻ and μ⁺μ⁻).

Main Results:

• No significant evidence for signal was observed in any of the searched decay channels.
• New upper limits at the 90% confidence level were set for the branching fractions, ranging from (3.8–47)×10⁻⁸.
• These limits represent the world's best results for these specific decay channels.

Conclusions:

• The absence of signal in these FCNC decays places stringent constraints on potential contributions from new physics.
• The established upper limits provide valuable data for theoretical models aiming to explain particle physics phenomena.
• This study marks the first search for B→(ω,ρ⁺,⁰)e⁺e⁻ and B→(ω,ρ⁺)μ⁺μ⁻ decays, expanding the experimental landscape.