SIMPLISTIC CARTOON. “The original quark model, in which the proton consists of two up quarks (u) and one down (d) quark, has an appealing simplicity, but experiments that measure the distributions of quarks as a function of the fractional momentum (x) of the proton that these quarks carry have revealed a rich structure with additional quarks, antimatter quarks (antiquarks) and gluons, beyond the minimal three-quark Fock state.”
https://www.nature.com/articles/s41586-021-03282-z