  We present an antenna-shower formalism that includes helicity dependence for
massless partons. The formalism applies to both traditional (global) showers
and to sector-based variants. We combine the shower with VINCIA's
multiplicative approach to matrix-element matching, generalized to operate on
each helicity configuration separately. The result is a substantial gain in
computational speed for high parton multiplicities. We present an
implementation of both sector and global showers, with min and max variations,
and helicity-dependent tree-level matching applied for vector bosons or Higgs
decay to q qbar plus up to 4 gluons and for Higgs decay to up to 5 gluons.
