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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).

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, a spin of ​32, and an isospin of ​32. Ordinary protons and neutrons (nucleons (symbol N)), by contrast, have a mass of about 939 MeV/c2, a spin of ​12, and an isospin of ​12. The
Δ+
(uud) and
Δ0
(udd) particles are the higher-mass excitations of the proton (
N+
, uud) and neutron (
N0
, udd), respectively. However, the
Δ++
and
Δ
have no direct nucleon analogues.

The states were established experimentally at the University of Chicago cyclotron[1] and the Carnegie Institute of Technology synchro-cyclotron[2] in the mid-1950s using accelerated positive pions on hydrogen targets. The existence of the
Δ++
, with its unusual +2 charge, was a crucial clue in the development of the quark model.

The Delta states discussed here are only the lowest-mass quantum excitations of the proton and neutron. At higher masses, additional Delta states appear, all defined by having ​32 units of isospin, but with a spin quantum numbers including ​12, ​32, ​52, ... ​112. A complete listing of all properties of all these states can be found in Ref.[3].

There also exist antiparticle Delta states with opposite charges, made up of the corresponding antiquarks.

Contents

Formation and DecayEdit

The Delta states are created when an energetic-enough probe such as a photon or pion impinges upon a proton or neutron, or possibly by the collision of an energetic-enough nucleon pair.

All of the Δ baryons with mass near 1232 MeV quickly decay via the strong force 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 and more slowly, the
Δ+
can decay into a proton and a photon and the
Δ0
can decay into a neutron and a photon.

ListEdit

Delta baryons
Particle
name
Symbol Quark
content
Mass
(MeV/c2)
I3 JP Q(e) S C B′ T Mean lifetime
(s)
Commonly
decays to
Delta[3]
Δ++
(1232)

u

u

u
1,232 ± 2 +​32 32+ +2 0 0 0 0 (5.63±0.14)×10−24[a]
p+
+
π+
Delta[3]
Δ+
(1232)

u

u

d
1,232 ± 2 +​12 32+ +1 0 0 0 0 (5.63±0.14)×10−24[a]
π+
+
n0
, or


π0
+
p+

Delta[3]
Δ0
(1232)

u

d

d
1,232 ± 2 −​12 32+ 0 0 0 0 0 (5.63±0.14)×10−24[a]
π0
+
n0
, or


π
+
p+

Delta[3]
Δ
(1232)

d

d

d
1,232 ± 2 −​32 32+ −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.

ReferencesEdit

  1. ^ H. L. Anderson, E. Fermi, E. A. Long, and D. E. Nagle, “Total Cross Sections of Positive Pions in Hydrogen.” Phys. Rev., 85, 936 (1952). and ibid. p. 934.
  2. ^ J. Ashkin et al., “Pion Proton Scattering at 150 and 170 MeV.” Phys. Rev., 101, 1149 (1956).
  3. ^ a b c d e J. Beringer et al. (2013): Particle listings –
    Δ
    (1232)

BibliographyEdit

  • C. Amsler et al. (Particle Data Group) (2008). "Review of Particle Physics". Physics Letters B. 667 (1): 1. Bibcode:2008PhLB..667....1A. doi:10.1016/j.physletb.2008.07.018.