Quantum Chromodynamics 2025, 50 - The Hadron Spectrum

I really just want a refresher on the topic, and maybe catch up with some fun exercises while I'm at it. For that, I'm using the book by Greiner, Schramm and Stein. Find a 1995 version of the book on archive.org here. I'm going to use and cite the third edition of the book, since that's what I have.

Quantum Chromodynamics presupposes knowledge of quarks and at least some quantum field theory, and I will do the same, mostly out of laziness. From this emerges the classification of particles into baryons and leptons. Baryons are (stable) particles that contain quarks, and leptons are stable particles that don't. The symmetries in classical and quantum mechanics go back to conserved quantum numbers. These are the Baryon number B, isospin T with its z-component T₃, strangeness S, hypercharge Y = B + S, charge Q + T₃ + Y/2, spin I with its z-component, parity π and charge conjugation parity π_c. These quantum numbers are subject to conservation laws across decays. The n → p + e^- and n → γ + γ don't exist, although the should be allowed by all other conservation law, so a new quantum number is inferred. p and n are set to have a baryonic charge B = 1 and leptonic charge L = 0, and e^- has B = 0 and L = 1. This initially implies an elementary-ness to all observed particles (p. 1). Baryons are classified as composed of fundamental particles - quarks - and their resonances are excitations of a few ground states. Hadrons are (unweighted) linear combinations of SU(3) states. Along with the quark spin direction, the total symmetry of the group is SU(3) × SU(2) (p.2). By construction, quarks have B = 1/3 and electric charges in multiples of ± 1/3 (p. 10).