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

TL;DR

This paper analyzes CP violation in $B_{(s)} o ext{phi}K$ decays within the Standard Model, providing predictions for CP asymmetries and proposing new decay channels to test for potential new physics effects.

Contribution

It offers theoretical predictions for CP asymmetries in $B_{(s)} o ext{phi}K$ decays using a factorization approach and introduces the $B_s^0 o ext{phi}K_S$ decay as a new probe for hadronic effects and new physics.

Findings

Predicted CP asymmetries for $B^0_d o ext{phi}K_S$ and $B_s^0 o ext{phi}K_S$ decays.

Derived constraints on isospin observables within the Standard Model.

Outlined potential signals of new physics in $B o ext{phi}K$ decays.

Abstract

The penguin loop-suppressed $B\to\phi K$ 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 $B^0_d\to\phi K_{\rm S}$ 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 $B_s^0\to\phi K_{\rm S}$ decay as a new channel. We predict the observables for this decay for which currently no measurements exist. By comparing $B^0_d\to\phi K_{\rm S}$ and $B^+ \to \phi K^+$, 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.