Tau

Tau (uppercase Τ, lowercase τ; Greek: ταυ [taf]) is the 19th letter of the Greek alphabet. In the system of Greek numerals it has a value of 300.

The name in English is pronounced /taʊ/ or /tɔː/, but in modern Greek it is [taf]. This is because the pronunciation of the combination of Greek letters αυ has changed from ancient to modern times from one of [au] to either [av] or [af], depending on what follows (see Greek orthography).

Tau was derived from the Phoenician letter taw (𐤕). Letters that arose from tau include Roman T and Cyrillic Te (Т, т).

The letter occupies the Unicode slots U+03C4 (lowercase) and U+03A4 (uppercase). In HTML, they can be produced with named entities (τ and Τ), decimal references (τ and Τ), or hexadecimal references (τ and Τ).

Modern usage

The lower-case letter τ is used as a symbol for:

Biology

Tauá

Tauá is a municipality in the state of Ceará in the Northeast region of Brazil. In 2010 it had a total population of 55,755 people. It is one of the largest municipalities in the state, with an area of 4,018.188 square kilometres (1,551.431 sq mi).

History

The toponymy of Tauá refers to an indigenous word meaning "yellow clay and loam" in the Tupi language. Its origins date from at least the early 18th century. On December 14, 1801, Ouvidor Gregório José da Silva went to the small settlement of Tauá to raise the site to a town. On May 3, 1802, it became a formal settlement. On August 17, 1832, it was given freguesia status. On December 2, 1889, the site was renamed São João do Príncipe dos Inhamuns. It received the classification of city on August 2, 1929, returning to its former name.

Geography

The city is located 337 kilometres (209 mi) away from the capital of Ceará State, Fortaleza. The town lies along BR-020, 60.8 kilometres (37.8 mi) by road northeast of Parambu. Districts of the municipality include Marrecas, Barra Nova, Trici, Marruás, Carrapateiras, Inhamuns, and Santa Tereza. The Jaguaribe River's headwaters are located in the Tauá districts of Trici and Carrapateiras. At Tauá, the Jaguaribe is rather narrow, 50–100 metres (160–330 ft) in width, and is sandy. The course of the river between Tauá to the mouth of the Salgado River is approximately 250 kilometres (160 mi).

Tau (particle)

The tau (τ), also called the tau lepton, tau particle, or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of ¹⁄₂. Together with the electron, the muon, and the three neutrinos, it is a lepton. Like all elementary particles with half-integral spin, the tau has a corresponding antiparticle of opposite charge but equal mass and spin, which in the tau's case is the antitau (also called the positive tau). Tau particles are denoted by τ− and the antitau by τ+.

Tau leptons have a lifetime of 6987290000000000000♠2.9×10⁻¹³ s and a mass of 7003177682000000000♠1776.82 MeV/c² (compared to 7002105700000000000♠105.7 MeV/c² for muons and 6999511000000000000♠0.511 MeV/c² for electrons). Since their interactions are very similar to those of the electron, a tau can be thought of as a much heavier version of the electron. Because of their greater mass, tau particles do not emit as much bremsstrahlung radiation as electrons; consequently they are potentially highly penetrating, much more so than electrons. However, because of their short lifetime, the range of the tau is mainly set by their decay length, which is too small for bremsstrahlung to be noticeable: their penetrating power appears only at ultra high energy (above PeV energies).