All hadrons (mesons and baryons) are
composed of particles called QUARKS.
Quarks have fractional electric charge compared with the charge on the electron of -e.
Their existence was confirmed by high energy electron scattering from the
nucleons.
We will only consider two types of quark here:
Up quark with a
charge +2/3 e
Down quark with a charge - 1/3 e
Baryons such as protons and neutrons are made of three quarks. The quarks are held together to form a larger particle by the strong force produced by the exchange of gluons between them.
Proton | up up down | uud | charge = +2/3 +2/3 -1/3 = +1 | ||
Neutron | down down up | ddu | charge = -1/3 -1/3 +2/3 = 0 |
Mesons are composed of one quark and one anti-quark. For example a p+ meson is composed of one up quark and one anti-down quark.
Electrons and neutrinos contain no quarks, they are truly fundamental particles themselves.
When you try and drag a quark out of a particle the strong force field between the quarks gets
bigger and bigger – rather like the force in a rubber band as it is stretched.