A | B | C | D | E | F | G | H | CH | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
Composition |
|
---|---|
Statistics | Fermionic |
Interactions | Strong, weak, 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 subatomic particle made of three up or down quarks (u or d quarks), the same constituent quarks that make up the more familiar protons and neutrons.
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 spins, additional higher mass Delta states appear, all defined by having constant 3 /2 or 1 /2 isospin (depending on charge), but with spin 3 /2, 5 /2, 7 /2, ..., 11 /2 multiplied by ħ. A complete listing of all properties of all these states can be found in Beringer et al. (2013).[1]
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 Carnegie Institute of Technology synchro-cyclotron[4]
in the mid-1950s using accelerated positive pions on hydrogen targets. The existence of 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 |
Mass (MeV/c2) |
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 | 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 | 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 | 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 | π− + n0 |
^ PDG reports the resonance width (Γ). Here the conversion is given instead.
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. Bibcode:1952PhRv...85..936A. doi:10.1103/PhysRev.85.936.
- ^ 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. Bibcode:1952PhRv...85..934H. doi:10.1103/PhysRev.85.934.
- ^ 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. Bibcode:1956PhRv..101.1149A. doi:10.1103/PhysRev.101.1149. hdl:2027/mdp.39015095214600.
Bibliography
- Amsler, C.; et al. (Particle Data Group) (2008). "Review of Particle Physics" (PDF). Physics Letters B. 667 (1): 1–6. Bibcode:2008PhLB..667....1A. doi:10.1016/j.physletb.2008.07.018. hdl:1854/LU-685594. S2CID 227119789. Archived from the original (PDF) on 2020-09-07. Retrieved 2019-12-11.
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