Direct CKM determination from W decays at future lepton colliders

TL;DR

Future lepton colliders, exemplified by FCC-ee, can significantly improve direct measurements of CKM matrix elements from W decays, with sensitivity heavily influenced by systematic uncertainties in jet flavor tagging.

Contribution

This work projects the potential of future lepton colliders to measure CKM elements directly from W decays, highlighting the importance of jet flavor tagging performance.

Findings

Future colliders can enhance CKM element sensitivity.

Jet flavor tagger performance impacts measurement precision.

Systematic uncertainties limit achievable accuracy.

Abstract

We project the reach of future lepton colliders for measuring CKM elements from direct observations of $W$ decays. We focus our attention to $|V_{cs}|$ and $|V_{cb}|$ determinations, using FCC-ee as case study. We employ state-of-the-art jet flavor taggers to obtain the projected sensitivity, and scan over tagger performances to show their effect. We conclude that future lepton collider can sizeably improve the sensitivity on $|V_{cs}|$ and $|V_{cb}|$, albeit the achievable reach will strongly depend on the level of systematic uncertainties on tagger parameters.