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A hadron is a composite subatomic particle.Every hadron must fall into one of the two fundamental classes of particle, bosons and fermions. In particle physics, a hadron (/ ˈ h æ d r ɒ n / ⓘ; from Ancient Greek ἁδρός (hadrós) 'stout, thick') is a composite subatomic particle made of two or more quarks held together by the strong interaction.
In particle physics, a lepton is an elementary particle of half-integer spin (spin 1 / 2 ) that does not undergo strong interactions. [1] Two main classes of leptons exist: charged leptons (also known as the electron-like leptons or muons), including the electron, muon, and tauon, and neutral leptons, better known as neutrinos.
In cosmological models of the Big Bang, the lepton epoch was the period in the evolution of the early universe in which the leptons dominated the mass of the Universe.It started roughly 1 second after the Big Bang, after the majority of hadrons and anti-hadrons annihilated each other at the end of the hadron epoch. [1]
Quarks are the fundamental constituents of hadrons and interact via the strong force. Quarks are the only known carriers of fractional charge , but because they combine in groups of three quarks (baryons) or in pairs of one quark and one antiquark (mesons), only integer charge is observed in nature.
Owing to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons (such as protons and neutrons) and mesons, or in quark–gluon plasmas. [2] [3] [nb 1] For this reason, much of what is known about quarks has been drawn from observations of hadrons.
In physical cosmology, the hadron era [1]: 209 is said to have begun at a time of 10-44 seconds, or at 10-8 seconds [2], and ended at 10-4 seconds. The temperature was high enough to allow the formation of hadron/anti-hadron pairs, which kept matter and anti-matter in thermal equilibrium .
The set of particles believed today to be elementary is known as the Standard Model and includes quarks, bosons and leptons. The term "subnuclear zoo" was coined or popularized by Robert Oppenheimer in 1956 at the VI Rochester International Conference on High Energy Physics. [3]
A blackbody is completely characterized by its temperature; the shift is called the redshift denoted by z: = (+) where 2.7 K is today's temperature. The thermal energy at the peak of the blackbody spectrum is the Boltzmann constant , k B , times the temperature, k B T CMB ( z ) {\displaystyle k_{B}T_{\text{CMB}}(z)} but simply comparing this to ...