In which direction is the spin of longitudinally polarized W?

[franoisbelfor]

I am simply curious: does "longitudinal polarization" for a W mean that the spin axis of the W is along the direction of motion? Or does it mean something else?

Thank you for any help!

FB

 

[blechman]

It could mean many things in principle. The standard basis (known as the "helicity" basis) is exactly what you said. Sometimes it is useful to define other definitions of polarization depending on what you're doing. But in typical papers, yes, this is what they mean.

 

[franoisbelfor]

Thank you! Now it is clearer where the unitarity problem that is cured by
the Higgs is supposed to appear.

François

 

[Vanadium 50]

I'm afraid this isn't quite right. The spin of a longitudinal W is transverse to its direction of motion (as counter-intuitive as this sounds).

 

[franoisbelfor]

It could mean many things in principle. The standard basis (known as the "helicity" basis) is exactly what you said. Sometimes it is useful to define other definitions of polarization depending on what you're doing. But in typical papers, yes, this is what they mean.

I'm afraid this isn't quite right. The spin of a longitudinal W is transverse to its direction of motion (as counter-intuitive as this sounds).

Oh! That would probably mean the spin precesses, always at an angle of 90 degrees, around the axis of motion. And that the spin axis in and against the direction of motion are the transversal polarisations.

Is that correct now?

François

 

[franoisbelfor]

Now I am completely confused. The HERA collider had polarized electrons, and they call
longitudinally polirezed electrons those with "spin" (?) in the direction of motion, as can be seen on many Powerpoint presentations online.

On teh other hand, it makes sense to say that spin in direction of motion is similar to helicity, thus similar to transversal polarization.

Who can help clearing up my confusion? Thank you in advance!

François

 

[Vanadium 50]

The convention for electrons is different for W's. It is confusing.