Δ-baryon
Delta baryon (Δ ++ , Δ + , Δ 0 , Δ - ) |
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classification | |
Fermion Hadron Baryon |
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properties | |
electric charge | 2, 0 or ± 1 e (+3.204 · 10 −19 C , 0 or ± 1.602 · 10 −19 C ) |
Resting energy | ≈1232 MeV |
Spin parity | 3/2 + |
Isospin | 3/2 (z component ± 3/2, ± 1/2) |
Decay width | ≈118 MeV |
Quark composition |
uuu, uud, udd, ddd |
The Δ-baryons ( delta baryons ) or delta resonances are baryons , which consist of up and down quarks . They have spin and isospin 3/2.
There are four different Δ-baryons, which are usually characterized by their electrical charge: Δ ++ , Δ + , Δ 0 and Δ - .
Δ + and Δ 0 consist of the same quarks as the nucleons protons and neutrons and can therefore be interpreted as their spin excitation .
It was discovered as the first pion nucleon resonance in 1951 at the cyclotron in Chicago by Herbert L. Anderson , Enrico Fermi , EA Long and Darrah E. Nagle . A resonance was observed at an energy of the pions scattered on protons of about 180 M eV . It was explained by Keith Brueckner using the isospin model of pions and nucleons.
description
The four-Δ baryons include the SU (3) - decuplet on. They differ in their quark content, which can be viewed abstractly as an isospin 3/2 vector in the flavor space. The quark content of the Δ-baryons is
symbol Curd content Isospin -z component Δ ++ uuu +3/2 Δ + uud +1/2 Δ 0 udd −1/2 Δ - ddd −3/2
Almost 100% of the Δ-baryons decay into a nucleon and a pion . A very small proportion (<1%) decays into a nucleon when a photon is emitted.
particularities
If one only considers the spin and flavor components, the Δ-baryons Δ ++ and Δ - seem to be a violation of the Pauli principle . As fermions , they should have an anti-symmetrical wave function , their spin and flavor wave functions however, they are completely symmetrical, e.g. B.
- ,
where stands for up-quark and + for the spin projection.
This problem can be solved by postulating another degree of freedom for quarks, the so-called color charge . If you introduce this new quantum number , you get
with the Levi-Civita symbol and the degrees of freedom and (green, blue, red). So the wave function is again anti-symmetric.
The Δ-baryons contributed to the development of quantum chromodynamics .
Today, the Δ-baryons are still of theoretical interest, since, analogous to the ρ-mesons , models of the dynamics of the strong force can be tested on them.
See also
Individual evidence
- ↑ The information on the particle properties (info box) are, unless otherwise stated, taken from: K. Nakamura et al. ( Particle Data Group ): Review of Particle Physics. In: Journal of Physics G , 37, 2010, 075021, lbl.gov
- ^ HL Anderson, E. Fermi, EA Long, DE Nagle: Total Cross Sections of Positive Pions in Hydrogen . In: Phys. Rev. , Volume 85, 1952, p. 936, princeton.edu (PDF)
- ↑ Darrah E. Nagle: The Delta - the first pion nucleon resonance , LALP 84-27. (PDF) Los Alamos National Laboratory; after a lecture in honor of Herbert Anderson at the University of Chicago in 1982.
- ↑ N. Nakamura et al . (2010): Particle listings - Δ (PDF; 70 kB)
- ↑ F. Yndurain: The Theory of quarks and gluon interactions . 4th edition. Springer, 2006, ISBN 3-540-64881-X .