BNL Physics Colloquia

The dance of the muon

by Prof. Aida X. El-Khadra (Univ. of Illinois at Urbana-Champaign)


More than eighty years after the muon was first identified it may become a window to discovering new physics. In April 2021, the Fermilab experiment announced, to worldwide media attention, a new measurement of the muon’s magnetic moment with an exquisite precision of 352 parts per billion, sharpening the longstanding tension between experiment and theory to a tantalizing 4.2 standard deviations. The experimental measurements will continue to improve with the ultimate goal of reducing the uncertainties by a factor of four. The theoretical calculations of the muon’s magnetic moment must account for the virtual effects of all particles and forces within the Standard Model, where effects coming from virtual hadrons, governed by the strong interactions, are the by far largest sources of theory uncertainty. I will discuss the ongoing interplay between theory and experiment that is essential to unlocking the discovery potential of this effort. 

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