EFT at JADE: a case study

As we use the standard model effective field theory to search for signs of new physics beyond the direct reach of the LHC, we often wonder what we may learn from the effective field theory, and what it would look like to make a discovery via effective field theory. This article presents a case study that provides some answers to these questions. We apply the low-energy effective field theory to $e^+e^- \to \mu^+\mu^-$ data below the Z boson mass from the JADE experiment at DESY. The low-energy effective field theory allows the observation of physics beyond QED in the JADE data and furthermore, by matching the Wilson coefficients to the electroweak theory, a rough measurement of the masses of the W and Z bosons is possible. The ability to make this rough measurement challenges the conventional wisdom that an observation of new physics via EFT tells us nothing about the nature of that new physics. A measurement of this quality would have been sufficient to guide the construction of colliders such as the super proton-antiproton synchrotron or the large electron-positron collider, and so we anticipate that a discovery of new physics via effective field theory at the LHC would be similarly sufficient to guide the construction of future colliders.