# Massless Dirac fermions vs helical Dirac fermions

Some papers when, dealing with graphene, write about charge carriers called helical Dirac fermions that have a conical energy–dispersion relation and a conserved quantity $$\sigma\cdot k$$ (pseudospin–pseudomomentum). To me this is the same as the standard massless Dirac particles (of graphene) but I'm not sure. Is it?