Baryons Baryons are massive particles consisting of three quarks in the standard model. Protons, neutrons and the lambda, sigma, xi, and omega particles are baryons. Baryons are distinct from mesons in that mesons are composed of only two quarks. Baryons and mesons, being subject to the strong force, are all members of the family of hadrons. Baryons are fermions - having spin 1/2 and subject to the Pauli exclusion principle - while the mesons are bosons, with spin 1, and not subject to the exclusion principle. All particle interactions obey the 'Law if Conservation of Baryon Number', in addition to the other conservation laws. The conservation of baryon number is an important rule for interactions and decays of baryons. No known interactions violate conservation of baryon number. Recent experimental evidence shows the existence of five-quark combinations which are being called pentaquarks. The pentaquark would be included in the classification of baryons,being a combination of an ordinary baryon plus a meson, having a 'net quark number' of three.