Topness

Topness (symbol T) or truth is a flavour quantum number that represents the difference between the number of top quarks (t) and number of top antiquarks (t) present in a particle:

${\displaystyle T=n_{\text{t}}-n_{\bar {\text{t}}}}$

By convention, top quarks have a topness of +1 and top antiquarks have a topness of −1. The term "topness" is rarely used; most physicists simply refer to "the number of top quarks" and "the number of top antiquarks".