Quark mixing from muon collider neutrinos

TL;DR

This paper explores how a high-energy muon collider can be used as a precise neutrino scattering experiment to measure the CKM quark mixing matrix, surpassing current limitations and offering new insights into parton distribution functions.

Contribution

It proposes using a muon collider's neutrino beam for high-precision measurements of quark mixing and parton distributions, highlighting its potential for significant advancements.

Findings

Potential for sensitivity improvements over current standards

Assessment of uncertainties from PDFs and fragmentation functions

Prospects for combined PDF determination

Abstract

A high energy muon collider naturally produces a collimated beam of neutrinos for a fixed-target experiment at a dedicated far-forward facility. The high intensity and energy of the beam makes it ideally suited for astonishingly precise measurements of neutrino scattering on nucleons in the deeply inelastic regime, enabling the determination of the Cabibbo--Kobayashi--Maskawa~(CKM) quark mixing matrix. We assess the floor to the attainable sensitivity set by irreducible sources of uncertainties from the imperfect knowledge of the parton distribution (PDF) and fragmentation functions, showing that a strong improvement is possible well above current standards. As a by-product, our analysis also outlines extraordinary perspectives for a combined determination of the PDF. The results demonstrate the potential of a parasitic neutrino experiment at the muon collider, motivating detailed future studies.