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Delta baryon

Family of subatomic particles

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Source updated December 4, 2025

The Delta baryons (or Δ baryons, also called Delta resonances) are a family of subatomic particle made of three up and/or down quarks, the same constituent quarks that make up the more familiar protons and neutrons.

01Properties

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 $\;I_{3}=\pm {\tfrac {1}{2}}~{\mathsf {or}}~\pm {\tfrac {3}{2}}\;;$ 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).

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

02Discovery

The states were established experimentally at the University of Chicago cyclotron and the Carnegie Institute of Technology synchro-cyclotron 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.

03Formation 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.

04List

Delta baryons
Particle name	Symbol	Quark content	Mass (MeV/c²)	I₃	J^P	Q (e)	Mean lifetime (s)	Commonly decays to
Delta	Δ⁺⁺ (1 232)	uuu	1232±2	+⁠ 3 /2⁠	⁠ 3 /2⁠⁺	+2	(5.63±0.14)×10⁻²⁴^{^[a]}	p⁺ + π⁺
Delta	Δ⁺ (1 232)	uud	1232±2	+⁠1/ 2 ⁠	⁠ 3 /2⁠⁺	+1	(5.63±0.14)×10⁻²⁴^{^[a]}	π⁺ + n⁰ , or π⁰ + p⁺
Delta	Δ⁰ (1 232)	udd	1232±2	⁠−+1/ 2 ⁠	⁠ 3 /2⁠⁺	0	(5.63±0.14)×10⁻²⁴^{^[a]}	π⁰ + n⁰ , or π⁻ + p⁺
Delta	Δ⁻ (1 232)	ddd	1232±2	⁠−+ 3 /2⁠	⁠ 3 /2⁠⁺	−1	(5.63±0.14)×10⁻²⁴^{^[a]}	π⁻ + n⁰

^[a] ^ PDG reports the resonance width (Γ). Here the conversion ${\textstyle \tau ={\frac {\hbar }{\Gamma }}$ is given instead.

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Sources and credits

This article is adapted from the Wikipedia article “Delta baryon”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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