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Q & A: Are the photon and gluon different beasts?

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Most recent answer: 11/16/2012
There something that troubles me. If a photon and a gluon have both same spin, no mass, no electric charge and are their own antiparticle, what makes them different? Is there any secret caracteristic that we are unaware of that makes them behave differently (electromagnetic force carrier VS color charge carrier)? Thanks
- Anonymous
Yes they are quite different.   The photon is a gauge boson carrier of the electric field.  The gluon is a gauge boson carrier of the color field.   Although they both have spin one and are mass-less they are quite different in other respects.  They have different coupling constants and strengths.  There is only one kind of photon whereas there are eight kinds of gluons, each having different combinations of color charge although each combination is color neutral.  See:  for lots of good info.


(published on 06/17/2010)

Follow-Up #1: Helicity of W-bosons in Top Quark decays

In the W boson helicity of the top quark decay the left handed helicity values is 0.30 , the longitudinal helicity is 0.70 while the right helicity come to 0.00, Now my question is that why the right handed helicity value is zero? is this values is due to v-a structure ? or it is due to the zero b mass in the top quark decay?
- Qasim Ali (age 27)
It's the V-A interaction.  In the standard model (SM), the top quark decays via the V −A weak charged-current interaction, which strongly suppresses right-handed W+ bosons or left-handed W− bosons.
If you are interested in gory experimental details, see:


(published on 11/16/2012)

Follow-up on this answer.