Boson (Bose particle), a particle or quasiparticle with zero or integer spin. Bosons obey Bose — Einstein statistics (hence the name of the particle). The bosons include photons (spin 1), gravitons (spin 2), mesons and boson resonances, composite particles made up of an even number of fermions (particles with half-integer spin), for example atomic nuclei with an even total number of protons and neutrons (the deuteron, the 4He nucleus and so on), the molecules of gases, and also phonons in a solid and in liquid 4He, excitons in semiconductors and dielectrics. The intermediate vector bosons and the gluons are also bosons.