Search for B --> tau(nu) and B --> K(nu)nu.

Area of Science:

• High Energy Physics
• Particle Physics
• Experimental Physics

Background:

• The Standard Model of particle physics predicts branching fractions for rare B meson decays.
• Understanding these decays provides insights into fundamental particle interactions and potential new physics.
• Previous searches for B --> tau(nu) and B --> K(nu)nu have constrained theoretical models.

Purpose of the Study:

• To search for the decay B --> tau(nu) using a large sample of charged B meson decays.
• To set an upper limit on the branching fraction of B --> tau(nu).
• To establish an upper limit for the branching fraction of B --> K(nu)nu.

Main Methods:

• Analysis of 9.7 x 10^6 charged B meson decays.
• Exclusive reconstruction of the companion B meson decay to effectively suppress background.
• Statistical analysis to determine upper limits at a 90% confidence level.

Main Results:

• An upper limit on the branching fraction for B --> tau(nu) was set at less than 8.4 x 10^-4.
• An upper limit on the branching fraction for B --> K(nu)nu was established at less than 2.4 x 10^-4.
• These results provide stringent constraints on new physics scenarios.

Conclusions:

• The experimental search places important limits on rare B meson decays.
• The findings are consistent with Standard Model predictions but leave room for new physics contributions.
• Further studies with larger datasets are needed to probe even smaller branching fractions.