  Superradiant Rayleigh scattering in a Bose gas released from an optical
lattice is analyzed with incident light pumping at the Bragg angle for resonant
light diffraction. We show competition between superradiance scattering into
the Bragg mode and into end-fire modes clearly leads to suppression of the
latter at even relatively low lattice depths. A quantum light-matter
interaction model is proposed for qualitatively explaining this result.
