Search for the rare decays B-->Kl(+)l(-) and B-->K(*)l(+)l(-)

Area of Science:

• Particle Physics
• High Energy Physics
• Experimental Physics

Background:

• Flavor-changing neutral current (FCNC) decays are rare but sensitive probes of new physics beyond the Standard Model.
• Understanding B meson decays provides insights into the fundamental properties of quarks and leptons.

Purpose of the Study:

• To search for FCNC decays B --> Kl+l- and B --> K*l+l- using a large dataset of Upsilon(4S) decays.
• To set upper limits on the branching fractions of these rare decays and compare them with theoretical predictions.

Main Methods:

• Analysis of 22.7 x 10^6 Upsilon(4S) --> B-B decays collected by the BABAR detector.
• Selection criteria applied to identify B --> Kl+l- and B --> K*l+l- decay modes, where l+l- is an e+e- or mu+mu- pair.
• Statistical analysis to determine upper limits at 90% confidence level.

Main Results:

• The 90% C.L. upper limits for the branching fractions were found to be B(B --> Kl+l-) < 0.51 x 10^-6 and B(B --> K*l+l-) < 3.1 x 10^-6.
• These experimental limits are close to the predictions of the Standard Model for these decay modes.
• Limits were also established for lepton-family-violating decays B --> Ke+/-mu(-/+) and B --> K*e(+/-)mu(-/+)

Conclusions:

• The experimental search places stringent constraints on the branching fractions of FCNC B meson decays.
• The results are consistent with the Standard Model, providing no evidence for new physics contributions to these processes.
• The study also constrains the possibility of lepton flavor violation in B meson decays.