Wiktionary
up quarks
n. (plural of up quark English)
Usage examples of "up quarks".
This has been inevitable since the minute we figured out how to break up quarks en masse without a cyclotron.
When a proton decays, two up quarks and one down quark turn into a positron (which goes off and annihilates the first electron it comes across) and a quark-antiquark pair (which is to say a meson).