Cosmic timeline 08

Simulation of a super-symmetry event (showing leptons and missing transverse energy), with a Higgs particle decaying to two Z particles and to four muons in the full Compact Muon Solenoid detector. The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors built on the proton-proton Large Hadron Collider (LHC) at CERN in Switzerland and France.

The Lepton Epoch
The lepton epoch is defined as the time between 1 second and 10 seconds after the Big Bang. The majority of hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving leptons and anti-leptons dominating the mass of the universe.

What is a lepton?
Leptons are a family of elementary particles, alongside quarks and gauge bosons. The name lepton comes from the Greek λεπτός or leptos, meaning thin, and was first used by physicist Léon Rosenfeld in 1948. So the name implies that all the leptons are of small mass. The first lepton identified was the electron, discovered by J.J. Thomson and his team of British physicists in 1897. Then in 1930, Wolfgang Pauli postulated the electron neutrino. Before the muon was discovered by Carl D. Anderson in 1936, the electron neutrino was simply known as the neutrino, as it was not yet known that neutrinos came in different flavours (or different “generations”). Then the tauon was first detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl. Like quarks, leptons are fermions and are subject to the electromagnetic force, the gravitational force, and weak interaction, but unlike quarks, leptons do not participate in the strong interaction.

Approximately 10 seconds after the Big Bang the temperature of the universe falls to the point where new lepton/anti-lepton pairs are no longer created and most leptons and anti-leptons are eliminated in annihilation reactions, leaving a small residue of leptons.

So far our timeline pages have covered only the first 10 seconds of the Big Bang theory of the origins of our universe, but from this point the timeline of subsequent epochs begins to stretch for hundreds of thousands of years.

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