The Physics Case for the New Muon (g-2) Experiment

TL;DR

The paper advocates for a new muon (g-2) experiment to refine measurements, potentially confirming new physics beyond the standard model by reducing experimental and theoretical uncertainties.

Contribution

It provides an updated review of the muon (g-2) status, emphasizing the need for improved precision and discussing the implications for new physics theories.

Findings

Current deviation is 3.4 sigma, suggesting possible new physics.

Proposed experiment aims to improve precision by a factor of 2.

Enhanced measurements could reach above 6 sigma sensitivity.

Abstract

This White Paper briefly reviews the present status of the muon (g-2) experiment and the physics motivation for a new effort. The present comparison between experiment and theory indicates a tantalizing $3.4 \sigma$ deviation. An improvement in precision on this comparison by a factor of 2--with the central value remaining unchanged--will exceed the ``discovery'' threshold, with a sensitivity above $6 \sigma$. The 2.5-fold reduction improvement goal of the new Brookhaven E969 experiment, along with continued steady reduction of the standard model theory uncertainty, will achieve this more definitive test. Already, the (g-2) result is arguably the most compelling indicator of physics beyond the standard model and, at the very least, it represents a major constraint for speculative new theories such as supersymmetry or extra dimensions. In this report, we summarize the present experimental status and provide an up-to-date accounting of the standard model theory, including the expectations for improvement in the hadronic contributions, which dominate the overall uncertainty. Our primary focus is on the physics case that motivates improved experimental and theoretical efforts. Accordingly, we give examples of specific new-physics implications in the context of direct searches at the LHC as well as general arguments about the role of an improved (g-2) measurement. A brief summary of the plans for an upgraded effort complete the report.