Every particle has a corresponding antiparticle. Compared with its particle, an antiparticle has:
• the same mass (the same rest energy)
• the opposite charge
• opposite values of the other quantum numbers, such as baryon number and lepton numberSo if you know the properties of a particle, you can deduce those of its antiparticle, and the other way round.Examples:
• electron e- (charge –1e) and positron e+ (charge +1e), both 0.511 MeV/c2
• proton p (charge +1e, baryon number +1) and antiproton p (charge –1e, baryon number –1), both 938 MeV/c2
• neutron n and antineutron n: both have zero charge, but opposite baryon numbers (+1 and –1)
• neutrino ν and antineutrino ν: both neutral, with opposite lepton numbersAntiparticles are usually written with a bar over the symbol, or for charged leptons by changing the sign of the charge (e+). A photon is its own antiparticle.The positron was predicted by Dirac in 1928 and discovered in cosmic ray tracks in 1932: it left a track like an electron's but curving the opposite way in a magnetic field.Worked example: a muon has mass 106 MeV/c2, charge –1e and lepton number +1. Its antiparticle, the antimuon, has mass 106 MeV/c2, charge +1e and lepton number –1.When particles and antiparticles are created or destroyed, they appear or disappear in pairs, as the next lessons show.
• the same mass (the same rest energy)
• the opposite charge
• opposite values of the other quantum numbers, such as baryon number and lepton numberSo if you know the properties of a particle, you can deduce those of its antiparticle, and the other way round.Examples:
• electron e- (charge –1e) and positron e+ (charge +1e), both 0.511 MeV/c2
• proton p (charge +1e, baryon number +1) and antiproton p (charge –1e, baryon number –1), both 938 MeV/c2
• neutron n and antineutron n: both have zero charge, but opposite baryon numbers (+1 and –1)
• neutrino ν and antineutrino ν: both neutral, with opposite lepton numbersAntiparticles are usually written with a bar over the symbol, or for charged leptons by changing the sign of the charge (e+). A photon is its own antiparticle.The positron was predicted by Dirac in 1928 and discovered in cosmic ray tracks in 1932: it left a track like an electron's but curving the opposite way in a magnetic field.Worked example: a muon has mass 106 MeV/c2, charge –1e and lepton number +1. Its antiparticle, the antimuon, has mass 106 MeV/c2, charge +1e and lepton number –1.When particles and antiparticles are created or destroyed, they appear or disappear in pairs, as the next lessons show.