Rare B decays in Belle II and LHCb

Rare b-hadron decays serve as valuable probes for exploring physics beyond the Standard Model. I will provide an overview of measurements related to rare radiative, leptonic, and semileptonic b-hadron decays conducted by two leading B-physics experiments currently active. The first experiment is the LHCb, situated at a proton-proton collider near Geneva, Switzerland, while the second is the Belle II experiment, located at an electron-positron collider in Tsukuba, Japan. In recent years, certain rare b-hadron-decay measurements have revealed tensions in observables sensitive to effects beyond the Standard Model. In this presentation I will particularly focus on the intriguing recent measurement by Belle II of the decay rate of B⁺→K⁺νν̄ process, which in the Standard Model is rather precisely predicted. Towards the end, I will also outline future plans aimed at further investigating beyond the Standard Model physics through the rare b-hadron decays in both experiments.