The LHCb collaboration at CERN's Large Hadron Collider (LHC) recently published a study Evidence For the Rare Decay B⁺→ ¯Λp¯μ⁺μ^- in Physical Review Letters.

Professor Sun Liang's team from Wuhan University (WHU)'s School of Physics and Technology played a significant role in this research.

The study of rare decays of heavy flavor hadrons, especially those involving flavor-changing neutral currents, is a crucial area in particle physics for exploring new physics beyond the Standard Model.

Recent LHCb studies on B→K()ℓ+ℓ− decays have garnered significant attention worldwide. In contrast, the B⁺→ ¯Λp¯μ⁺μ^- decay, which also involves the b→sℓ+ℓ− transition, has been less explored both theoretically and experimentally.

This decay offers valuable dynamical information and provides additional observables to detect potential new physics effects. Furthermore, it offers a clean platform to study the ¯Λp hadron system, enhancing our understanding of highly excited strange mesons and exotic states like X(2085).

However, the branching fraction of B⁺→ ¯Λp¯μ⁺μ^- is two orders of magnitude lower than mesonic processes like B→K()μ+μ-, and the presence of a long-lived Λ hyperon in the final state poses significant experimental challenges.

Utilizing proton-proton collision data from LHCb's second run (Run 2, 2016-2018) and employing machine learning techniques, this study provides the first evidence of the rare baryonization decay process B⁺→ ¯Λp¯μ⁺μ^-.

The signal's significance near the ¯Λp invariant mass production threshold is 3.5σ and the measured branching fraction is on the order of 10^-8, consistent with previous Standard Model predictions within two standard deviations.

The study also sets an upper limit of 10^-9 for the partial branching fraction in the high ¯Λp invariant mass region, supporting the threshold enhancement mechanism for baryon pair production, offering critical experimental input for theoretical studies of B meson to baryon pair hadronization form factors and paving the way for future theoretical and experimental work in B meson baryonization rare decays.

Since joining the LHCb collaboration in 2016 as the fourth Chinese university in this international effort, WHU has made significant strides in high-energy physics, particularly in the study of rare B meson decays and charmless baryonic final state decays.