Delta baryon

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The Delta baryon is a relatively light 1,232 MeV/c² baryon which contains only up (u) and down (d) quarks in a combination whose total spin is 3/2 and its ground state parity is +.

[edit] Decay

All varieties of Δ quickly decay via the strong force into an ordinary nucleon plus a pion. Any combination of nucleon and pion whose charges sum to match the Δ is equally likely. More rarely and more slowly, the Δ⁺ can decay into a proton and a photon and the Δ⁰ can decay into neutron and a photon.

[edit] Composition

The 3/2 spin means that all the quarks inside a Δ particle have their spin axes pointing in the same direction, unlike the nearly identical proton and neutron (called "nucleons") in which the intrinsic spin of one of the three constituent quarks is always opposite the spin of the other two. This difference in spin alignment is the only quantum number distinction between the Δ⁺ and Δ⁰ and ordinary nucleons, whose spin is 1/2.

The Δ family consists of four different particles distinguished by their electrical charges, which is the sum of the charges of the mixture of up (u) and down (d) quarks which compose the Δ:

Particle	Symbol	Makeup	Rest mass MeV/c2	S	C	B	Mean lifetime s	Decays to
Delta	Δ++	uuu	1232	0	0	0	6×10-24	π+ + p
Delta	Δ+	uud	1232	0	0	0	6×10-24	π+ + n or π0 + p
Delta	Δ0	udd	1232	0	0	0	6×10-24	π0 + n or π- + p
Delta	Δ-	ddd	1232	0	0	0	6×10-24	π- + n

There are also four antiparticles with opposite charges, made up of the corresponding antiquarks.

The existence of the Δ⁺⁺, with its unusual +2 charge, was a crucial clue in the development of the quark model.

[edit] See also

• List of baryons
• particle physics
• quark model