In
particle physics, isospin multiplets are families of
hadrons with approximately equal masses. All particles within a multiplet, have the same
spin
Spin or spinning most often refers to:
* Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning
* Spin, the rotation of an object around a central axis
* Spin (propaganda), an intentionally b ...
, parity, and baryon numbers, but differ in electric charges.
Isospin formally behaves as an
angular momentum operator and thus satisfies the appropriate canonical commutation relations. For a given isospin quantum number I, 2I + 1 states are allowed, as if they were the third components of an angular momentum operator Î. The set of these states is called ''isospin multiplet'' and is used to accommodate the particles.
An example of an isospin multiplet is the nucleon multiplet consisting of the
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
and the
neutron. In this case I = 1/2 and by convention the proton corresponds to the I
3 = +1/2, while the neutron to I
3 = -1/2. Another example is given by the
delta baryons. In this case I = 3/2.
The existence of the multiplets with approximately equal masses owes to the fact that the masses of up and down
quarks are approximately equal
[http://pdg.lbl.gov/2017/reviews/rpp2017-rev-quark-masses.pdf ] (compared to a typical hadron mass), and the strong interaction is
quark flavour blind. This makes the ''
isospin symmetry'' a good approximation.
References
Hadrons
{{Particle-stub