Correction

We wish to clarify our recent news story about an important sign correction in the standard-model calculation of the muon’s anomalous magnetic moment (see February 2002, page 18 ). We were remiss in failing to make clear the central role of Marc Knecht, Andreas Nyffeler, and colleagues at the University of Marseille, in being the first to discover—and make a convincing case—that the long-accepted sign of the hadronic light-by-light scattering contribution to the anomalous moment was wrong. Last November, Knecht and Nyffeler reported a detailed analytic and numerical calculation (ref. 3 in our story) that yielded the correct sign. Furthermore, in an accompanying paper with Michel Perrottet and Eduardo de Rafael (our ref. 4), they clinched the case for the corrected sign with an effective-field-theory approach to the hadronic light-by-light scattering. We also apologize to those who may have taken offense to our reference to the prevalent use of the Pauli metric in the Netherlands as an “ethnic idiosyncracy [sic].”