Why do we need the new BNL muon g-2 experiment now?

TL;DR

The paper discusses the importance of the new BNL muon g-2 experiment, which aims to reduce experimental uncertainty and clarify the current discrepancy with the standard model, potentially revealing new physics beyond the standard model.

Contribution

It outlines the necessity and plans for the BNL E969 experiment to significantly lower the muon g-2 measurement uncertainty, enhancing the search for new physics.

Findings

Current discrepancy of 3.3 sigma suggests possible new physics

Recent data-driven improvements have reduced theoretical uncertainty below experimental levels

Proposed experiment aims to halve the experimental uncertainty, increasing sensitivity to new physics

Abstract

New final results from the CMD-2 and SND e+e- annihilation experiments, together with radiative return measurements from BaBar, lead to recent improvements in the standard model prediction for the muon anomaly. The uncertainty at 0.48 ppm--a largely data-driven result--is now slightly below the experimental uncertainty of 0.54 ppm. The difference, a_mu(expt)- a_mu(SM) = (27.6 +/- 8.4) x 10^-10, represents a 3.3 standard deviation effect. At this level, it is one of the most compelling indicators of physics beyond the standard model and, at the very least, a major constraint for speculative new theories such as SUSY or extra dimensions. Others at this Workshop detailed further planned standard model theory improvements to a_mu. Here I outline how BNL E969 will achieve a factor of 2 or more reduction in the experimental uncertainty. The new experiment is based on a proven technique and track record. I argue that this work must be started now to have maximal impact on the interpretation of the new physics anticipated to be unearthed at the LHC.