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Particle Physics - Classification, 3 of 3 Mesons     Interactions: Weak, electromagnetic, strong     Spin: Integral Name Symbol Mass (MeV/c2) Charge Lifetime (s) Spin Pion p+ 139.6 +1 2.6 x 10-8 0 Pion p0 135.0 0 8.4 x 10-17 0 Pion p- 139.6 -1 2.6 x 10-8 0 Kaon K+ 493.8 +1 1.2 x 10-8 0 Kaon K0 497.88 0 0.9 x 10-10 0 Rho r+ 770.0 +1 4.4 x 10-24 1 Upsilon U+ 9460.0 0 1.3 x 10-20 1 Only few examples of mesons are listed above. They are strongly interacting particle, produced in reactions by the strong interaction. Mesons are made of a quark and an antiquark. They usually decay through the strong, electromagnetic or weak interaction. For example, pions minus can be produced in reaction of nucleons: At first, with enough energy, reaction between a proton (p) and a neutron (n) can produce a pion minus, which then dacays into muon (a lepton) and an antineutrino. The presence of a neutrino indicate the decay occurs via the weak interaction. Baryons     Interactions: Weak, electromagnetic, strong     Spin: Half integral Name Symbol Mass (MeV/c2) Charge Lifetime (s) Spin Proton p 938.3 +1 stable 1/2 Neutron n 939.6 0 887 1/2 Sigma S+ 1189 +1 0.8 x 10-10 1/2 Xi X0 1315 0 2.9 x 10-10 1/2 Sigma star S*0 1193 0 1.8 x 10-23 3/2 Omega W- 1672 -1 8.2 x 10-11 3/2 Lambda b L0b 5624 0 1.2 x 10-12 1/2 Only some of the selected baryons are shown above. They are strongly interacting particle, consist of three quarks. Since only baryons and mesons are found to take part in strong interactions. They are also grouped together and called hadrons. In Greek it means strong.

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