Interference Effects in a Very Precise Measurement of the Muon Charge Asymmetry at FCC-ee

TL;DR

This paper investigates the interference effects in a high-precision measurement of muon charge asymmetry at FCC-ee, focusing on whether QED calculations can accurately account for and subtract these effects to improve fundamental constant measurements.

Contribution

It demonstrates the potential of resummed QED calculations to reliably compute and subtract interference effects in muon charge asymmetry measurements at FCC-ee.

Findings

Resummed QED calculations can accurately model interference effects.

Proper subtraction of interference effects enhances measurement precision.

Implications for precise determination of electromagnetic coupling at the Z scale.

Abstract

At the future high luminosity electron-positron collider FCC-ee proposed for CERN, the precise measurement of the charge asymmetry in $e^+ e^- \to \mu^+ \mu^-$ near the Z resonance is of special interest. In particular, such a measurement at $M_Z \pm 3.5$ GeV may provide a very precise measurement of the electromagnetic coupling at the scale $\sim M_Z$, a fundamental constant of the Standard Model. However, this charge asymmetry is plagued by a large trivial contribution from the interference of photon emission from initial state electrons and final state muons. We address the question whether this interference can be reliably calculated and subtracted with the help of a resummed QED calculation.