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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.
