Inquiring Minds


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You asked:

Why is the top quark so massive?


Dear High School Senior:

Well, that actually is a question that all physicists would like to be able to answer. The top quark is as heavy as a gold atom--yet it is an elementary particle that, to our present knowledge, cannot be split into subunits. (Be aware that until about 100 years ago, scientists didn't think they could split atoms into smaller subunits.)

How does the top quark gets its mass? Like all other particles, the top quark receives its mass by constantly interacting with the so-called Higgs field. You can find details on this topic by looking at http://www.fnal.gov/pub/inquiring/questions/higgs_boson.html

According to current theory, all particles would be massless if there would be no Higgs field. The Higgs field creates a drag for particles, like some sort of molasses. Some particles feel more of the drag (resulting in more mass), some less (less mass).

The deficiency of the Higgs model is the absence of predicting the mass of the various particle masses. Physicists need to put in the values for each particle by hand. The Higgs theory ACCOMMODATES the various particles and their different masses, but it DOES NOT PREDICT them. This is the most important reason why physicists believe that our current theory cannot be the ultimate answer. They suspect that there is an even more fundamental theory that would predict why a top quark is 350,000 times heavier than an electron.

Presently, physicists have little knowledge what a more predictive theory would look like. Discovering the Higgs particle, which is intimately connected to the Higgs field, and studying its properties will very likely provide information on the underlying mechanism, showing physicists the way to the right theory.

The particle accelerator LEP at the European physics laboratory CERN may have seen a glimpse of the Higgs boson in some of the very last experiments it did in September and October, 2000. The LEP experiments needed to be discontinued to make room for a more powerful particle accelerator called the LHC, which should easily be able to create the Higgs boson. The LHC will begin operation in 2005. In the meantime, Fermilab's Tevatron accelerator may have a chance at producing the Higgs particle if it is as light as the LEP experiments seem to indicate. This would be very fortunate since the Tevatron wasn't built to search for the Higgs particle but to discover and study the top quark, the most massive elementary particle physicists have ever found.

Best wishes,

Kurt Riesselmann


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last modified 11/9/2000   physicsquestions@fnal.gov