Eta meson

The eta (η) and eta prime meson (η′) are mesons made of a mixture of up, down and strange quarks and their antiquarks. The charmed eta meson (η
c) and bottom eta meson (η
b) are forms of quarkonium; they have the same spin and parity as the light eta but are made of charm quarks and bottom quarks respectively. The top quark is too heavy to form a similar meson, due to its very fast decay.

General

The eta was discovered in pion-nucleon collisions at the Bevatron in 1961 by A. Pevsner et al. at a time when the proposal of the Eightfold Way was leading to predictions and discoveries of new particles from symmetry considerations.

The difference between the mass of the η and that of the η' is larger than the quark model can naturally explain. This " η-η' puzzle" can be resolved by the 't Hooft instanton mechanism, whose 1/N realization is also known as Witten-Veneziano mechanism.

Quark composition

The η particles belong to the "pseudo-scalar" nonet of mesons which have spin J = 0 and negative parity, and η and η′ have zero total isospin, I, and zero strangeness and hypercharge. Each quark which appears in an η particle is accompanied by its antiquark (the particle overall is "flavourless") and all the main quantum numbers are zero.

Eta

Eta (uppercase Η, lowercase η; Ancient Greek: ἦτα êta or Modern Greek: ήτα íta) is the seventh letter of the Greek alphabet. Originally denoting a consonant /h/, its sound value in the classical Attic dialect of Ancient Greek was a long vowel [ɛː], raised to [i] in medieval Greek, a process known as iotacism.

In the system of Greek numerals it has a value of 8. It was derived from the Phoenician letter heth . Letters that arose from Eta include the Latin H and the Cyrillic letter И.

History

Consonant h

The letter shape 'H' was originally used in most Greek dialects to represent the sound /h/, a voiceless glottal fricative. In this function, it was borrowed in the 8th century BC by the Etruscan and other Old Italic alphabets, which were based on the Euboean form of the Greek alphabet. This also gave rise to the Latin alphabet with its letter H.

Other regional variants of the Greek alphabet (epichoric alphabets), in dialects that still preserved the sound /h/, employed various glyph shapes for consonantal Heta side by side with the new vocalic Eta for some time. In the southern Italian colonies of Heracleia and Tarentum, the letter shape was reduced to a "half-heta" lacking the right vertical stem (Ͱ). From this sign later developed the sign for rough breathing or spiritus asper, which brought back the marking of the /h/ sound into the standardized post-classical (polytonic) orthography.Dionysius Thrax in the second century BC records that the letter name was still pronounced heta (ἥτα), correctly explaining this irregularity by stating "in the old days the letter Η served to stand for the rough breathing, as it still does with the Romans."

ʻOkina

The ʻokina, also called by several other names, is a unicameral consonant letter used within the Latin script to mark the phonetic glottal stop, as it is used in many Polynesian languages.

Names

Appearance

The ʻokina visually resembles a left single quotation mark—a small "6"-shaped mark above the baseline.

The Tahitian ʻeta has a distinct shape, like an ʻokina turned 90° or more clockwise.

Orthography and official status

The ʻokina is a letter in the Hawaiian alphabet. It is unicameral, unlike the other letters (all of which are basic Latin letters). For words that begin with an ʻokina, capitalization rules affect the next letter instead (for instance, at the beginning of a sentence, the name of the letter is written "ʻOkina", with a capital O).

Geographic names in the United States

The United States Board on Geographic Names lists relevant place names both with and without the ʻokina and kahakō in the Geographic Names Information System. Colloquially and formally, the forms have long been used interchangeably.

Eta (given name)

Eta is a feminine given name. Notable people with the name include:

See also