Delta baryon
Composition |
|
---|---|
electromagnetic, and gravity | |
Symbol | Δ |
Types | 4 |
Mass | 1232±2 MeV/c2 |
Spin | 3 /2, 5 /2, 7 /2 ... |
Strangeness | 0 |
Charm | 0 |
Bottomness | 0 |
Topness | 0 |
Isospin | 3 /2 |
The Delta baryons (or Δ baryons, also called Delta resonances) are a family of
Properties
Four closely related Δ baryons exist:
Δ++
(constituent quarks: uuu),
Δ+
(uud),
Δ0
(udd), and
Δ−
(ddd), which respectively carry an electric charge of +2 e, +1 e, 0 e, and −1 e.
The Δ baryons have a mass of about 1232 MeV/c2; their third component of isospin and they are required to have an intrinsic spin of 3 /2 or higher (half-integer units). Ordinary nucleons (symbol N, meaning either a proton or neutron), by contrast, have a mass of about 939 MeV/c2, and both intrinsic spin and isospin of 1/ 2 . The
Δ+
(uud) and
Δ0
(udd) particles are higher-mass spin-excitations of the proton (
N+
, uud) and neutron (
N0
, udd), respectively.
The
Δ++
and
Δ−
, however, have no direct nucleon analogues: For example, even though their charges are identical and their masses are similar, the
Δ−
(ddd), is not closely related to the antiproton (
p
, uud).
The Delta states discussed here are only the lowest-mass quantum excitations of the proton and neutron. At higher
There also exist antiparticle Delta states with opposite charges, made up of the corresponding antiquarks.
Discovery
The states were established experimentally at the University of Chicago cyclotron[2][3] and the
Δ++
, with its unusual electric charge of +2 e, was a crucial clue in the development of the quark model
Formation and decay
The Delta states are created when a sufficiently energetic probe – such as a photon, electron, neutrino, or pion – impinges upon a proton or neutron, or possibly by the collision of a sufficiently energetic nucleon pair.
All of the Δ baryons with mass near 1232 MeV quickly decay via the strong interaction into a nucleon (proton or neutron) and a pion of appropriate charge. The relative probabilities of allowed final charge states are given by their respective isospin couplings. More rarely, the
Δ+
can decay into a proton and a photon and the
Δ0
can decay into a neutron and a photon.
List
Particle name |
Symbol | Quark content |
MeV/c 2)
|
I3 | JP
|
Q (e) |
S | C | B′ | T | Mean lifetime )
(s |
Commonly decays to |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Delta[1] | Δ++ (1 232) |
u u u |
1232±2 | + 3 /2 | 3 /2+ | +2 | 0 | 0 | 0 | 0 | (5.63±0.14)×10−24[a] | p+ + π+ |
Delta[1] | Δ+ (1 232) |
u u d |
1232±2 | +1/ 2 | 3 /2+ | +1 | 0 | 0 | 0 | 0 | (5.63±0.14)×10−24[a] | π+ + n0 , or π0 + p+ |
Delta[1] | Δ0 (1 232) |
u d d |
1232±2 | −+1/ 2 | 3 /2+ | 0 | 0 | 0 | 0 | 0 | (5.63±0.14)×10−24[a] | π0 + n0 , or π− + p+ |
Delta[1] | Δ− (1 232) |
d d d |
1232±2 | −+ 3 /2 | 3 /2+ | −1 | 0 | 0 | 0 | 0 | (5.63±0.14)×10−24[a] | π− + n0 |
[a]
References
- ^ a b c d e
Beringer, J.; et al. (Particle Data Group) (2013).
Δ
(1 232) (PDF) (Report). Particle listings. - ^ Anderson, H. L.; Fermi, E.; Long, E. A.; Nagle, D. E. (1 March 1952). "Total cross-sections of positive pions in hydrogen". Physical Review. 85 (5): 936. .
- ^ Hahn, T. M.; Snyder, C. W.; Willard, H. B.; Bair, J. K.; Klema, E. D.; Kington, J. D.; Green, F. P. (1 March 1952). "Neutrons and gamma-rays from the proton bombardment of beryllium". Physical Review. 85 (5): 934. .
- ^ Ashkin, J.; Blaser, J. P.; Feiner, F.; Stern, M. O. (1 February 1956). "Pion-proton scattering at 150 and 170 Mev". Physical Review. 101 (3): 1149–1158. .
Bibliography
- Amsler, C.; et al. (S2CID 227119789. Archived from the original(PDF) on 2020-09-07. Retrieved 2019-12-11.