Sizing Up the Top Quark’s Interaction with the Higgs

Among the most recently discovered elementary particles, the top quark and the Higgs boson may be our best bets to reach a deeper understanding of the laws of nature. That’s because both particles are outliers in the particle zoo. The top quark is similar to the up quark found in ordinary matter, but it is about one hundred thousand times heavier—with a mass close to that of a tungsten nucleus. The Higgs boson, meanwhile, is the only fundamental particle observed so far that doesn’t have the intrinsic property of spin. This attribute is essential to the Higgs boson’s role in the standard model, where it is tied to the mechanism that endows elementary particles with mass. The Compact Muon Solenoid (CMS) Collaboration at CERN’s Large Hadron Collider (LHC) now provides the most definitive measurement to date of the strength of the interaction between the Higgs boson and the top quark [1]. The measured value of this important parameter agrees with the standard model prediction. But the relatively large uncertainty (13%) leaves the door open to future measurements uncovering a discrepancy, which could lead to the resolution of mysteries surrounding the Higgs mechanism.