η meson

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η

classification
Boson
Hadron
Meson
properties
electric charge neutral
Resting energy 547,862 (18)  MeV
Spin parity 0 -
Isospin 0 (z component 0)
average lifespan 5.0 (2) · 10 −19  s
Decay width 0.00131 (5)  MeV
Interactions strong
weak
electromagnetic
gravitation
Quark
composition

η ′

properties
electric charge neutral
Resting energy 957.78 (6)  MeV
Spin parity 0 -
Isospin 0 (z component 0)
average lifespan 3.32 (15) · 10 −21  s
Decay width 0.198 (9)  MeV
Quark
composition

The η-meson (eta-meson) and the η′-meson (read: "eta-dash meson") are mesons . They are subject to the strong interaction and thus belong to the hadrons .

description

In the quark model, η and η ′ are a mixture of the three quark anti- quark states u u , d d and s s of the up, down and strange quarks. Both states η and η ′ have a hypercharge and an isospin and stand in the multiplet of the pseudoscalar mesons in the same place as the neutral pion .

The three mutually orthogonal linear combinations of the above Quark-antiquark states are identified as follows:

with the meson
with , an η-state in the -octet
with , an η-state in the singlet.

The physical ( mass ) states η and η ′ result in turn as linear combinations of η 8 and η 1 :

The mixing angle introduced in this way has an experimental value that is strongly model-dependent and lies between −10 ° and −20 °. The η meson therefore almost corresponds to the octet state η 8 , with an admixture of a few percent of the singlet state η 1 ; with the η′-meson it is the other way round

.

The η meson was first detected in 1961 at the Lawrence Radiation Laboratory in Pion - Deuteron reactions.

In the case of the flavors charm and bottomness , pseudoscalar mesons also occur, but because of the large mass of the c and b quarks they only mix little with the light quark states. The η c and η b are therefore practically pure quarkonium states c c and b b, respectively .

Decay channels

The η meson can decay through different channels ; most common are the decay into three pions (π + π - π 0 or 3 π 0 ) with around 55% and the decay into two photons with 39%. The decay into two pions is forbidden because it would violate the parity and also the CP invariance .

The main decay channels of the η ′ are the decay into one η meson and two pions (π + π - η or π 0 π 0 η) with a share of around 65% and the decay into ρ 0 γ or π + with a total of 29% π - γ.

literature

  • Francis Halzen, Alan Douglas Martin: Quarks and leptons: an introductory course in modern particle physics. 1st edition. Wiley, New York 1984, ISBN 0-471-88741-2 .

See also

Individual evidence

  1. a b The information on the particle properties (info box) are taken from: J. Beringer et al. ( Particle Data Group ): 2013 Review of Particle Physics. In: Physical Review D . Vol. 86, 2012, 010001 and 2013 partial update for the 2014 edition. Particle Data Group, accessed May 22, 2018 .
  2. Reviews - Quark Model (PDF; 644 kB) from K. Nakamura et al. ( Particle Data Group ): Review of Particle Physics. In: Journal of Physics G 37 (2010) 075021.
  3. ^ A. Pevsner et al .: Evidence for a three-pion resonance near 550 Mev. In: Physical Review Letters . Vol. 7, No. 11, 1961, pp. 421-423, doi : 10.1103 / PhysRevLett.7.421 .