Search for the Decays B_{s}^{0}→τ^{+}τ^{-} and B^{0}→τ^{+}τ^{-}.

Area of Science:

• Particle Physics
• High Energy Physics
• Standard Model Physics

Background:

• Rare meson decays provide sensitive probes of fundamental physics beyond the Standard Model.
• The decays B_{s}^{0}→τ^{+}τ^{-} and B^{0}→τ^{+}τ^{-} are predicted to have very small branching fractions within the Standard Model.
• Experimental searches for these decays are challenging due to their predicted rarity and the complex final state.

Purpose of the Study:

• To search for the rare decays B_{s}^{0}→τ^{+}τ^{-} and B^{0}→τ^{+}τ^{-}.
• To set direct upper limits on the branching fractions of these decays.
• To constrain new physics scenarios that could enhance these rare processes.

Main Methods:

• Analysis of proton-proton collision data collected by the LHCb detector.
• Integrated luminosity of 3 fb^{-1} from 2011 and 2012 data.
• Reconstruction of tau leptons via the decay channel τ^{-}→π^{-}π^{+}π^{-}ν_{τ}.

Main Results:

• An upper limit on the branching fraction B(B_{s}^{0}→τ^{+}τ^{-})<6.8×10^{-3} at the 95% confidence level was set, assuming no contribution from B^{0}→τ^{+}τ^{-} decays.
• An upper limit on the branching fraction B(B^{0}→τ^{+}τ^{-})<2.1×10^{-3} at the 95% confidence level was set, assuming no contribution from B_{s}^{0}→τ^{+}τ^{-} decays.
• These results represent the first direct limit on B(B_{s}^{0}→τ^{+}τ^{-}) and the world's best limit on B(B^{0}→τ^{+}τ^{-}).

Conclusions:

• The study provides stringent constraints on the branching fractions of B_{s}^{0}→τ^{+}τ^{-} and B^{0}→τ^{+}τ^{-} decays.
• The obtained limits are competitive with theoretical expectations and probe new physics scenarios.
• This search contributes to the ongoing effort to understand flavor physics and search for deviations from the Standard Model.