Precision physics at the muon collider: $m_W$ and CKM matrix elements

TL;DR

This paper explores the potential of a 10 TeV muon collider for precision measurements of the W boson mass and CKM matrix elements, emphasizing detector development for improved hadronic energy resolution.

Contribution

It identifies the hadronic decay channel as promising for surpassing current CKM element measurement precision and highlights the importance of detector advancements.

Findings

Hadronic channel can improve CKM measurements over current methods.

Detector response understanding can determine CKM elements, especially for heavy quarks.

High-precision hadronic energy measurements are crucial for future collider experiments.

Abstract

We examine the potential for a 10~TeV lepton collider to carry out precision measurements of the W boson mass and W boson couplings strength, i.e. the CKM matrix elements. We consider the several W boson production mechanisms and focus on the most copious at 10~TeV, that is effective $\gamma W \to W$, a process viable at both opposite sign and same-sign leptonic colliders. We find that the leptonic W decay channel can hardly be competitive with present determinations, due to lack of rate. The hadronic channel has potential to improve over the current $\simeq$10~MeV from measurements at hadron colliders, motivating detector developments towards high-precision hadronic energy measurements. We find that the precision understanding of the detector response to hadrons can also lead to a determination of the CKM matrix elements. We expect determination of CKM matrix elements surpassing by far the present precision for couplings involving heavy quarks, notably $V_{cb}$, avoiding the present bottle-necks due to poor knowledge of hadronic matrix elements needed in low energy extractions of CKM matrix elements. Our findings motivate detector developments towards high-precision hadronic energy measurements and flavor tagging.