Associate 1995-96

Tony M Liss


Understanding the Top Quark

The recent evidence for top quark production at Fermilab culminates a 17-year search for the partner to the bottom quark. Over the next year, Professor Liss and his team expect to increase the dataset by about a factor of ten, and this affords them the first opportunity to probe the detailed properties of this heaviest of all known elementary particles. With the increase in statistics, they hope to improve the accuracy of their measurement of the top mass by almost a factor of two. A precision measurement of the top mass will provide the first, indirect, measurement of the mass of the Higgs boson, an undiscovered particle which is supposed to be responsible for the generation of the masses of other particles. One of the outstanding questions of particle physics today is why the particle masses are what they are, and the indirect measure of the Higgs mass may be the beginning of the answer to that question.

Because of the extremely large mass of the top quark, it provides a unique window to new physics. By detailed studies of the production and decay modes of the top quark, it is possible to probe potential new physics and potentially uncover what lies beyond current understanding. An excess in the production rate of top quarks over expectations can signal a new production mechanism via the decay of a new heavy particle. Decays of the top quark into unexpected channels is another way to uncover new physics.

Professor Liss and his team also hope, with increased statistics, to observe for the first time the production of single top quarks (as opposed to the more common top pair production) through a process known as "W-gluon fusion." Although the observation of this production mode will be difficult, a measurement of the rate of production through this mode will provide the first direct measurement of the lifetime of the top quark.