New theoretical research suggests that studying the decays of the Lambda_b (Λ_b⁰) baryon could offer a pathway to detect the presence of massive invisible fermions. These fermions, which do not interact with known fundamental forces except gravity, are candidates for dark matter components or exotic particles beyond the Standard Model. The study focuses on the Λ_b⁰ → Λ_c⁺ ℓ⁻ X̄_inv decay, where ℓ is a charged lepton (electron or muon) and X̄_inv represents the invisible particle. The key lies in the fact that the mass of this invisible particle would leave a distinctive "fingerprint" on the angular distribution of the decay products, allowing it to be distinguished from massless particles like standard neutrinos.

The analysis is based on a model-independent weak effective theory, which gives it broad applicability. Researchers have shown that a detailed angular analysis of the decay products can reveal whether the invisible particle is massive or not. Furthermore, these angular observables would not only allow inferring the mass of the invisible particle but also provide crucial information about the nature of the underlying interaction. This includes the ability to distinguish between vector/axial-vector, scalar/pseudoscalar, and tensor interactions, as well as between left- and right-handed quark and lepton current operators.

The ability to discriminate between different types of interactions is fundamental for characterizing any new physics. If deviations from predictions for massless invisible particles (like neutrinos) were observed, it would indicate the existence of new particles or interactions. This approach complements current efforts in direct dark matter searches and collider experiments, offering a new window to explore the universe's dark sector through heavy baryon decays. The results of this theoretical work open the door for future experimental investigations at accelerators, such as the LHC, which could search for these signatures in B baryon decay data.