|Flavour in particle physics|
|Flavour quantum numbers:
Related quantum numbers:
The weak hypercharge in particle physics is a conserved quantum number relating the electrical charge and the third component of weak isospin, and is similar to the Gell-Mann–Nishijima formula for the hypercharge of strong interactions (which is not conserved). It is frequently denoted YW and corresponds to the gauge symmetry U(1).
It is the generator of the U(1) component of the electroweak gauge group, SU(2)xU(1) and its associated quantum field B mixes with the W3 electroweak quantum field to produce the observed Z0 gauge boson and the photon of quantum electrodynamics.
Weak hypercharge, usually written as YW, is defined as:
Note: sometimes weak hypercharge is scaled so that
although this is a minority usage.
Baryon and lepton number 
Weak hypercharge is related to baryon number - lepton number via:
where X is a GUT-associated conserved quantum number. Since weak hypercharge is also conserved this implies that baryon number minus lepton number is also conserved, within the Standard Model and most extensions.