quarks

• elementary fermions (spin 1/2) that make up hadrons, e.g. protons (uud) and neutrons (udd)
• 6 flavours in 3 generations: up/down, charm/strange, top/bottom
• electric charge +2/3 (u, c, t) or −1/3 (d, s, b)
• colour charge (red, green, blue): the charge of the strong interaction
• the only elementary particles that feel all four fundamental interactions
• confinement: never seen alone, only in colour-neutral combinations (baryons: three quarks, mesons: quark + antiquark)
• asymptotic freedom: nearly free at very short distances
• heavier flavours decay into lighter ones via the weak interaction
• masses from ~2 MeV/c² (up) to ~173 GeV/c² (top)
• top quark: decays in ~5 × 10⁻²⁵ s, before it can form hadrons (toponium reported at the LHC in 2025: CMS Collaboration, ATLAS Collaboration)