Final answer:
Lepton and baryon numbers are conserved in particle physics interactions. Total lepton number is constant, but neutrino oscillations can change individual lepton family numbers. Baryon number conservation ensures that baryons decay into other baryons, and thus the sum of the baryon numbers before and after an interaction remains constant.
Step-by-step explanation:
Lepton and baryon numbers are quantum numbers assigned to particles that express conservation laws in particle physics. The conservation of these numbers means that the sum of the lepton or baryon numbers before and after a reaction or decay process must remain constant.
The conservation of lepton number refers to the principle that in a closed system, the total lepton number (denoted as L) does not change during an interaction. Leptons have a lepton number L = +1, antileptons have L = -1, and all other particles have L = 0. Although the total lepton number is conserved, experiments have shown that the individual lepton family numbers (like electron lepton number Le) can change due to a process known as neutrino oscillations.
Baryon number conservation is a rule stating that the sum of baryon numbers in a system remains unchanged in any interaction. Baryons, such as protons and neutrons, have a baryon number B = +1, antibaryons have B = -1, and other particles, like mesons and leptons, have B = 0. Mesons can decay into leptons without violating baryon number conservation because mesons do not carry a baryon number. However, baryons must always decay into another baryon, thus maintaining the conservation of the baryon number.
Both conservation laws are essential in predicting and explaining the outcomes of particle interactions and decays. For example, the decay of a neutron into a proton must be accompanied by the creation of an electron and an electron anti-neutrino to conserve both charge and baryon number, resulting in a process known as beta decay.