Opportunities at FCC-ee for quark & lepton flavour physics

Abstract

The FCC-ee phase of a Future Circular Collider is generating great interest due to its versatility, allowing the study of various electroweak thresholds, $Z$, $WW$, $ZH$, and $t \bar{t}$. Electroweak precision physics is complemented by flavour physics measurements based on the unprecedented statistics attainable at the $Z$ pole, and benefiting from the low-background experimental environment (similar to Belle II), and from the production of the full spectrum of hadron species together with large boosts (similar to LHCb). A wide range of measurements is possible, spanning a rich variety of physics cases in both quark and lepton flavour physics sectors. Other electroweak thresholds can also be considered in this endeavour. A commensurate effort from the theory community will be needed to interpret future measurements. I present an overview of the broad potential of the FCC-ee flavour physics program.

Figures (1)

• Figure 1: Bounds on the relative sizes of NP with respect to the SM (for which $h_d=h_s=0$) in the $B_d$ and $B_s$ meson systems. Current bounds reach $\sim 20\%$. Phase I ($\sim$ 2030’s) corresponds to Belle II 10/ab & LHCb 50/fb; Phase II ($\sim$ 2040’s) to Belle II 50/ab & LHCb 300/fb; and Phase III ($\sim$ 2050’s) corresponds to Phase II, together with improvements from FCC-ee. The different observables used in these fits are considered to perfectly agree.