Mesons are hadrons composed of a quark-antiquark pair. They are bosons, meaning they have integer spin, i.e., 0, 1, or −1, as they have an even number of quarks. They have baryon number B = ​1⁄3 − ​1⁄3 = 0. Examples of mesons commonly produced in particle physics experiments include pions and kaons. Pions also play a role in holding atomic nuclei together via the residual strong force.