Press Room

From the Nature press release:

Physics: The mass of the top quark (June 10, 2004; pp638-642; N&V)

The discovery of the top quark in 1995 provided dramatic confirmation of the essential validity of the standard model of particle physics. But there's a catch - the standard model contains parameters whose origins are still unknown and which cannot be predicted, but whose values are constrained by their interactions with other particles and fields. Something else is afoot. For example, the mass of the top quark is related to the mass of the long-hypothesized but still undetected Higgs boson. Properties of the (equally hypothetical) field associated with this particle would help explain why matter is, not to put too fine a point on it, 'massive'. In principle, the top quark is point-like and should have no mass; yet, through its interactions with the Higgs field, the physical mass of the top quark appears to be about that of a gold nucleus.

Because it is so heavy, the top quark provides an unusually sensitive tool for investigating the Higgs field. Well-constrained values for the top-quark mass will enable researchers to predict the mass of the Higgs particle, eliminating as untenable various theoretical fixes for deficiencies in the standard model, while supporting others. Much, therefore, rides on precision measurements of the top quark.

This is where the multinational Dě collaboration comes in: they have measured the mass of the top quark with unprecedented precision. Their value, 178 ▒ 4.3 GeV/c2 (where GeV/c2 represents gigaelectron volts divided by the square of the speed of light), is important because it raises the upper limit on the Higgs mass from 219 to 251 GeV/c2. The most likely value of the mass is now 117 GeV/c2; the previous value of 96 GeV/c2 falls in a range now ruled out by experiment. Further improvements in precision are to be expected from the Tevatron at Fermilab, and from the Large Hadron Collider at CERN (the European nuclear research laboratory at Geneva) when it becomes operational after 2007.

Georg Weiglein discusses the research in an accompanying News and Views article.

CONTACT: Greg Landsberg (Brown University, Providence, RI, USA) Tel: +1 401 863 1464, E-mail:

Georg Weiglein (University of Durham, UK)
Tel: +44 191 334 3520, E-mail:

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last modified 6/7/2004   email Fermilab