CP Violation in $B_{(s)} oϕK$ Decays: Standard Model Benchmarks and Isospin-Breaking New Physics

The penguin loop-suppressed $B\toϕK$ decays are highly sensitive to contributions of hypothetical heavy new particles. Particularly interesting probes for testing the Standard Model and revealing such phenomena are provided by CP violation in the $B^0_d\toϕK_{\rm S}$ decay. Standard-Model estimates for the corresponding CP-violating observables are theoretically limited by doubly Cabibbo-suppressed penguin contributions. We study these effects using a factorization approach, and provide predictions for CP asymmetries, to be contrasted with future measurements. To gain additional insight into these hadronic effects, we propose the $B_s^0\toϕK_{\rm S}$ decay as a new channel. We predict the observables for this decay for which currently no measurements exist. By comparing $B^0_d\toϕK_{\rm S}$ and $B^+ \to ϕK^+$, we further derive state-of-the-art constraints on isospin observables within the Standard Model. The same framework enables probing of possible New-Physics contributions, including general effects and those with non-trivial isospin structure. Interesting prospects arise for the high-precision era of flavour physics ahead.

💡 Research Summary

The paper investigates CP violation in the penguin‑dominated B→ϕK decay family, focusing on the neutral mode B⁰_d→ϕK_S and the yet‑unobserved B⁰_s→ϕK_S, and also on the charged mode B⁺→ϕK⁺. Because these decays proceed via the loop‑level b→s s̄ s transition in the Standard Model (SM), they are highly sensitive to heavy new‑physics (NP) particles that could appear in the loops. The dominant theoretical uncertainty in SM predictions for CP‑violating observables comes from doubly Cabibbo‑suppressed penguin contributions, which are usually neglected. The authors retain these contributions, parametrising the decay amplitude as

A(B→ϕK)=A′_P