View source for Topness

{{refimprove|date=September 2018}}
{{Flavour quantum numbers}}
<!--It would be interesting to know, why the name was changed.-->
'''Topness''' (symbol '''''T''''') or '''truth''' is a [[flavour quantum number]] that represents the difference between the number of [[top quark]]s (t) and number of [[top antiquark]]s ({{overline|t}}) present in a particle:
:<math>T = n_\text{t} - n_\bar{\text{t}}</math>

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

==Conservation==
Like all [[flavour quantum number]]s, topness is preserved under [[strong interaction|strong]] and [[electromagnetic interaction]]s, but not under [[weak interaction]]. However the top quark is extremely unstable, with a [[half-life]] under 10<sup>&minus;23</sup> s, which is the required time for the strong interaction to take place. For that reason the top quark does not [[hadronization|hadronize]], that is it never forms any [[meson]] or [[baryon]], so the topness of a meson or a baryon is always zero. By the time it can interact strongly it has already decayed to another flavour of quark (usually to a [[bottom quark]]).

==References==
* {{cite arXiv
 |last1=Anchordoqui  |first1=L.
 |last2=Halzen |first2=F.
 |authorlink2 = Francis Halzen
 |year=2009
 |title=Lessons in Particle Physics
 |eprint=0906.1271
 |class=physics.ed-ph
}}

==Further reading==
* {{cite arXiv
 |last1=Anchordoqui  |first1=L.
 |last2=Halzen |first2=F.
 |authorlink2 = Francis Halzen
 |year=2009
 |title=Lessons in Particle Physics
 |eprint=0906.1271
 |class=physics.ed-ph
}}

[[Category:Quarks]]
[[Category:Flavour (particle physics)]]


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