Originally Posted by **lekha** Why the W mesons are called 'vector' mesons? I know that its spin is 1, but what vector properties does it show to be called so? |

Just a quick note...The Ws (and Z) are not made up of quarks, so they can't be mesons. They are what is called "mediator" particles ie. those that are carriers of a given force. (In this case the weak nuclear force.) All mediator particles are bosons, as far as I know.

First the Lorentz group: this is the group for Special Relativity. We say that a particle has a certain property if it stays the same under a (Lorentz) transformation.

To give you a quick (and simpler) example, consider the cross product. Let us take the vector A and the vector B and look at C = A X B. If we do a "parity" transformation we take (x, y, z)

--> (-x, -y, -z). So the vector A goes to -A and the vector B goes to -B. What happens to A X B? Well we get (-A) X (-B) = C. But that means that the "vector" C does not go to -C under a parity transformation. So C isn't really a vector, it is a pseudo-vector.

So (finally!) to your question. Vectors transform in a certain way under Lorentz transformations. In this case the wavefunction for a W transforms as a vector does under Lorentz transformations.

-Dan