Ω-baryon

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Ω -

classification
Fermion
Hadron
Baryon
properties
electric charge −1  e
(−1.602 · 10 −19  C )
Resting energy 1672.45 (29)  MeV
magnetic moment −2.02 (5)  μ N
Spin parity 3 ⁄ 2 +
Isospin 0
Strangeness −3
average lifespan 0.821 (11) · 10 −10  s
Quark
composition 		sss
Quark structure omega.svg
Proof of the first Ω - (1964). The charged particles involved in production and decay left traces in the bubble chamber (shown here). Electrically neutral particles that were not visible in the detector are shown in dashed lines. A high energy K - hit a proton in the bubble chamber. An Ω - , a K + and a K 0 were generated. When the Ω - decayed , a π - and a Ξ 0 were created , which further decayed into a Λ 0 and a π 0 . The Λ 0 split into a proton and a π - ; the π 0 ( not visible here due to its short lifespan) decayed into two photons (γ), each generating an electron-positron pair .

The Ω-baryon, also known as the omega-baryon, is a relatively long-lived hadron that belongs to the group of baryons .

The particle was predicted in 1961 on the basis of theoretical considerations and experimentally demonstrated in 1964 in a bubble chamber at the Brookhaven National Laboratory . With its sss configuration, it has a strangeness of −3. It is the only known particle that consists of three heavy (i.e. not belonging to the first elementary particle family) quarks of the same flavor .

Generation and Decay

Since the strangeness quantum number is retained during the generation via the strong interaction , in addition to three s-quarks, three s- antiquarks would have to be generated when generating an Ω . This can be reduced to two s s pairs if one of the reaction partners is a K - ( kaon ) because it already contains an s quark. In order to maintain the number of baryons , the other reaction partner must be a baryon , the simplest being a proton (p). One possible reaction is:

K - ( u s) + p (uud) → Ω - (sss) + K + (u s ) + K 0 (d s )

For energetic reasons, the decay is only possible in particles with a total of less than three s-quarks and can therefore only occur via the weak interaction , e.g. B. by:

Ω - (sss) → Λ 0 (uds) + K - ( u s)
Ω - (sss) → Ξ 0 (uss) + π - ( u d)

Apparent violation of the Pauli principle

The particles (sss) presented introduction of color charge, similar to the - (uuu) and the particles (ddd), a violation of the Pauli principle is it given in all three particles to members of Baryonendekupletts with. Spin of  3 ⁄ 2 . Since quarks are fermions with spin  1 ⁄ 2 , the spins of the three quarks must be parallel so that the vector sum is 3 ⁄ 2 . This in turn means that the quarks are the same in all quantum numbers . This would imply that the omega’s wave function is symmetrical. The Pauli principle, however, requires an anti-symmetrical wave function for fermions.

The problem was solved by postulating an additional internal degree of freedom for quarks, the color charge . Thus the quarks differ again in at least one quantum number, and their wave functions are again anti-symmetric.

Ω c and Ω b

Heavy baryons have been detected that have a charm quark or a bottom quark instead of one of the s quarks , i.e. with the quark composition ssc and ssb . They are referred to as Ω c (or Ω c 0 ) or Ω b (or Ω b - ).

literature

See also

Individual evidence

  1. ↑ The information on the particle properties (info box) are, unless otherwise stated, 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. (No longer available online.) Particle Data Group, archived from the original on February 26, 2014 ; accessed on February 26, 2014 (English). .
  2. ^ A b V. E. Barnes et al .: Observation of a Hyperon with Strangeness Minus Three In: Physical Review Letters. Volume 12, 1964, p. 204 ( online )