Hadrons are particles made of quarks

Quarks, Leptons & Conservation Laws — AQA A-Level Physics

Key Definition

Hadrons — Particles composed of quarks. They are subject to the strong interaction.

Hadrons split into two sub-groups: baryons and mesons.
Baryons are made of 3 quarks. Mesons are made of a quark-antiquark pair.
Examples of baryons: proton ($p$), neutron ($n$), and their antiparticles.
Examples of mesons: pions ($\pi^{+}$, $\pi^{-}$, $\pi^{0}$) and kaons ($K^{+}$, $K^{-}$, $K^{0}$).

Baryons

All baryons have a baryon numberA quantum number conserved in all interactions. Baryons (protons, neutrons) have baryon number +1, antibaryons have -1, and mesons/leptons have 0. $B = +1$. All antibaryons have $B = -1$.
The proton is the only stable baryon. All other baryons eventually decay into protons.
A free neutron decays into a proton via $\beta^{-}$ decay with a half-lifeThe time taken for half the number of radioactive nuclei in a sample to decay, or for the activityThe number of nuclear decays per unit time. Measured in becquerels (Bq), where 1 Bq = 1 decay per second. to halve. of about 10 minutes.

Mesons

All mesons have baryon numberA quantum number conserved in all interactions. Baryons (protons, neutrons) have baryon number +1, antibaryons have -1, and mesons/leptons have 0. $B = 0$ (a quark and an antiquark cancel).
Pions ($\pi$) are the lightest mesons and act as exchange particles of the strong force between nucleons.
Kaons ($K$) are heavier mesons that contain a strange quark (or anti-strange quark).
Kaons decay into pions. Pions decay into muons and neutrinos.