neutron

Constituent particle of an atom’s nucleus whose electric charge is neutral; it is composed of one u quark and two d quarks.

d quark

The d quark (down) is one of six types of quarks (constituent particles of protons and neutrons) having a negative electric charge.

u quark

The u quark (up) is one of six types of quarks (constituent particles of the protons and neutrons) having a positive electric charge.

proton

Constituent particle of an atom’s nucleus whose electric charge is positive; it is composed of two u quarks and one d quark.