Abstract
The mixing of neutral mesons is sensitive to some of the highest scales probed in laboratory experiments. In light of the planned LHCb Upgrade II, a possible upgrade of Belle II, and the broad interest in flavor physics in the tera-$Z$ phase of the proposed FCC-ee program, we study constraints on new physics contributions to $B_d$ and $B_s$ mixings which can be obtained in these benchmark scenarios. We explore the limitations of this program, and identify the measurement of $|V_{cb}|$ as one of the key ingredients in which progress beyond current expectations is necessary to maximize future sensitivity. We speculate on possible solutions to this bottleneck. Given the current tension with the standard model (SM) in semileptonic $B$ decays, we explore how its resolution may impact the search for new physics in mixing. Even if new physics has the same CKM and loop suppressions of flavor changing processes as the SM, the sensitivity will reach 2 TeV, and it can be much higher if any SM suppressions are lifted. We illustrate the discovery potential of this program.
Highlights
The mixing of neutral mesons has provided severe constraints on new degrees of freedom at high energies: since measurements of mixing and CP violation in neutral kaons in the 1960s, it has provided precious information on charm and top quarks before their discovery
In light of the planned LHCb Upgrade II, a possible upgrade of Belle II, and the broad interest in flavor physics in the tera-Z phase of the proposed FCC-ee program, we study constraints on new physics contributions to Bd and Bs mixings which can be obtained in these benchmark scenarios
Given the current tension with the standard model (SM) in semileptonic B decays, we explore how its resolution may impact the search for new physics in mixing
Summary
The mixing of neutral mesons has provided severe constraints on new degrees of freedom at high energies: since measurements of mixing and CP violation in neutral kaons in the 1960s, it has provided precious information on charm and top quarks before their discovery. The FCC-ee phase of a future circular collider as a tera-Z factory is generating much interest, due to the versatility of the machine center-of-mass energy [16], which allows the study of all relevant electroweak thresholds (Z, WW, ZH, and tt) and addresses electroweak precision physics (Higgs physics, electroweak precision observables at Z pole and WW thresholds) in an unrivaled way, benefiting simultaneously from both the statistics and the exquisite measurement of the beam energy at the Z and WW thresholds This physics case is complemented by the unprecedented statistics attainable at the Z pole (Oð5 × 1012Þ Z decays) that can be used for flavor physics measurements, exploiting the clean experimental environment (similar to Belle II), and the production of all species of heavy flavors and the large boost (similar to LHCb).
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