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.
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.
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.
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.
Particle name |
Symbol | Quark content |
Mass ( MeV/ c2) |
I3 | J P |
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] ^ PDG reports the resonance width (Γ). Here the conversion is given instead.