The constituent quark model. History and new challenges for QCD

In 1960 particle physicists believed that the nucleon and pion were elementary Like the electron and the photon Nuclei were bound by a pion-exchange force Like atoms were bound by a photon-exchange force Today we know that hadrons are made of quarks which we believe are elementary Hadrons are bound by a gluon exchange force.

The journey from nucleons and pions to quarks and gluons First stage – there were too many hadrons 1. Gell-Mann and Ne’eman classified the nucleon and pion into SU(3) octets.

2. No reason for the number 3 in SU(3); No reason for octets 3. No reason why mesons and baryons should both be in octets 4. Mesons and baryons were very different, like electron and photon.


Slides (PDF)