Search for the rare decay B-->pil+ l-

Area of Science:

• Particle Physics
• High Energy Physics
• Quantum Chromodynamics

Background:

• Flavor-changing neutral-current (FCNC) decays are rare processes predicted by the Standard Model.
• Lepton flavor violation (LFV) is a phenomenon not explained by the Standard Model.
• B meson decays provide a sensitive probe for new physics beyond the Standard Model.

Purpose of the Study:

• To search for the FCNC decays B-->pil+l- (where l+l- is e+e- or mu+mu-).
• To search for the LFV decays B-->pie+/-mu-/+.
• To set upper limits on the branching fractions of these rare decays.

Main Methods:

• Analysis of 230 x 10^6 Upsilon(4S)-->BB decays collected by the BABAR detector.
• Event reconstruction and selection for B-->pil+l- and B-->pie+/-mu-/+ decay modes.
• Statistical analysis to set upper limits at 90% confidence level.

Main Results:

• No significant signal was observed for B-->pil+l- decays.
• An upper limit on the isospin-averaged branching fraction for B-->pil+l- was set at B(B-->pil+l-)<9.1 x 10^-8.
• No significant signal was observed for B-->pie+/-mu-/+ decays.
• An upper limit on the isospin-averaged branching fraction for B-->pie+/-mu-/+ was set at B(B-->pie+/-mu-/+)<9.2 x 10^-8.

Conclusions:

• The experimental results place stringent constraints on the branching fractions of B-->pil+l- and B-->pie+/-mu-/+ decays.
• These findings are consistent with Standard Model predictions for FCNC decays and place limits on potential new physics scenarios that could enhance LFV decays.
• The study contributes to the ongoing effort to precisely measure B meson properties and search for deviations from the Standard Model.