The Top Quark   

On March 2, 1995, Fermilab announced the discovery, ten days earlier, of the top quark, the last of the six predicted quarks.  The search had begun in 1977 when physicists found the fifth quark, the bottom quark, at Fermilab.  It had taken this long because the top quark is much more massive than had been originally predicted, so it required a more powerful accelerator to create it.

Although the top quark decays too fast to be observed, it does leave behind particles that give record to its existence - a top quark "signature".  The top quark can decay in more than one way.  Since a top quark appears only once in several billion collisions, it was necessary to perform trillions of collisions. 

Physicists still do not understand why the top is so massive.  It is 40 times more massive than the next most massive quark and about 35,000 times more massive than the up and down quarks that make up most of the matter we see around us.  In fact the question still remains why particles have such different masses.  Physicists hope that the discovery of the top quark will give them insight to such questions.
 
 

Top quark production from a proton/antiproton annihilation. Top quark production: View an animation of the event. Top quark production: Study a diagram of a real top event.