Observation of the decay B --> Kl+l-

Area of Science:

• Particle Physics
• High Energy Physics
• Experimental Particle Physics

Background:

• Flavor-changing neutral current (FCNC) decays are rare processes predicted by the Standard Model of particle physics.
• The decay B --> K(*)l+l- provides a sensitive probe for new physics beyond the Standard Model.
• Previous searches for this decay mode had not yet yielded a definitive observation.

Purpose of the Study:

• To search for the FCNC decay B --> K(*)l+l-, where l is an electron or muon.
• To measure the branching fraction of the observed decay process.
• To constrain new physics models by comparing experimental results with theoretical predictions.

Main Methods:

• Analysis of a 29.1 fb^-1 data sample collected by the Belle detector at the KEKB e+e- collider.
• Utilized data accumulated at the Upsilon(4S) resonance.
• Employed advanced event reconstruction and background suppression techniques to identify B --> Kl+l- candidates.

Main Results:

• First observation of the decay B --> Kl+l- (l = e, mu).
• Measured branching fraction B(B --> Kl+l-) = (0.75(+0.25)(-0.21) ± 0.09) x 10^-6.
• The observed significance and branching fraction provide valuable data for theoretical interpretations.

Conclusions:

• The first observation of B --> Kl+l- confirms theoretical predictions for FCNC decays.
• This result opens new avenues for studying rare B meson decays and searching for new physics.
• Future studies with larger datasets will further refine measurements and enhance sensitivity to new physics phenomena.