A joint Fermilab/SLAC publication

Top quark motto: Live fast, die young


Top quark lifetime

From today's issue of Fermilab Today:  

If you go to a high school track practice, you’ll see coaches using stop watches to time the young athletes. A world-class 100-yard dash can take just shy of 10 seconds and, for a time interval like that, a stop watch is entirely adequate. Of course there are things that are much faster, such as a blink of an eye or a beat of a hummingbird’s wings. But compared to the subatomic realm, these brief instants might as well be an eternity.

Most of the subatomic particles made at the Tevatron have a fleeting existence, but it is rare for one to live as briefly as the top quark. DZero scientists have announced that they have determined the lifetime of the top quark and found it to be an ephemeral 3 x 10-25 seconds. This is a mind-bogglingly tiny number, and there are no good analogies to describe something that small.

This result is accomplished by exploiting a principle of quantum mechanics, called the Heisenberg Uncertainty Principle. In its most basic form, it states that you can’t accurately know the position and the velocity of an object at the same time. However, a variant of the principle says that similarly you can’t accurately know simultaneously the energy and lifetime of a particle. Remember that Einstein showed that mass and energy are the same thing. DZero scientists were able to use subtle methods to determine a range of possible masses for top quarks and to therefore infer the particle’s lifetime.

Another interesting feature of this result is that it uses events in which a single top quark was produced. This accomplishment is particularly noteworthy because top quarks are most commonly produced in pairs and the first observation of events in which a single top quark was produced was a mere year ago. This new measurement dramatically underscores the ongoing process of scientific exploration, where one discovery leads to another.

Don Lincoln

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