Leaping into the Microscopic World: The Leptons Quiz

The lepton number conservation rule in particle interactions is that lepton numbers must be conserved. In particle interactions, the total lepton number before and after the interaction should remain the same. This conservation rule applies separately to each lepton family, meaning the conservation of electron lepton number, muon lepton number, and tau lepton number.

Leptons consist of six elementary particles. The particle that belongs to the lepton family is the electron. Electrons are elementary particles with a negative electric charge, and they are part of the first lepton family. 

The lepton number of an electron is 1. Lepton number is a quantum number that represents the number of leptons minus the number of antileptons in a system. Since an electron is a lepton, it has a lepton number of +1. Antileptons, such as positrons, would have a lepton number of -1. 

The property of leptons related to their intrinsic angular momentum is spin. In quantum mechanics, spin is an intrinsic form of angular momentum carried by elementary particles. Leptons, like all fermions, have a spin of 1/2.

Scientists know about three neutrino flavors so far: the electron neutrino, muon neutrino, and tau neutrino. These are related to the three charged lepton flavors: the electron, muon, and tau.

An electron neutrino is electrically neutral. It has a lepton number of +1 and no electric charge.

Among the three charged leptons, the tau lepton is the heaviest. The hierarchy of masses for the charged leptons, from lightest to heaviest, is electron, muon, and tau. Neutrinos, associated with each lepton flavor, have much smaller masses, and their specific masses are challenging to measure accurately.

Cosmic rays are primarily produced by the strong interaction. When cosmic rays enter the Earth’s atmosphere, they collide with atoms and molecules, mainly oxygen and nitrogen. The interaction produces a cascade of lighter particles, a so-called air shower secondary radiation that rains down, including x-rays, protons, alpha particles, pions, muons, electrons, neutrinos, and neutrons.

Cosmic rays are primarily composed of hadrons, specifically protons (hydrogen nuclei), which make up about 89% of cosmic rays. They also include helium nuclei (about 10%) and heavier atomic nuclei (about 1%).