  In this paper, a novel conserved Lorentz covariant tensor, termed the
helicity tensor, is introduced in Maxwell theory. The conservation of the
helicity tensor expresses the conservation laws contained in the helicity
array, introduced by Cameron et al., including helicity, spin, and the
spin-flux or infra-zilch. The Lorentz covariance of the helicity tensor is in
contrast to previous formulations of the helicity hierarchy of conservation
laws, which required the non-Lorentz covariant transverse gauge. The helicity
tensor is shown to arise as a Noether current for a variational symmetry of a
duality-symmetric Lagrangian for Maxwell theory. This symmetry transformation
generalizes the duality symmetry and includes the symmetry underlying the
conservation of the spin part of the angular momentum.
