  Polarized $\Lambda_b \to \Lambda \gamma$ decays at the Z pole are shown to be
well suited for probing a large variety of New Physics effects. A new
observable is proposed, the angular asymmetry between the $\Lambda_b$ spin and
photon momentum, which is sensitive to the relative strengths of the opposite
chirality and Standard Model chirality $b \to s \gamma$ dipole operators.
Combination with the $\Lambda $ decay polarization asymmetry and comparison
with the $\Lambda_b$ polarization extracted from semileptonic decays allows
important tests of the $V-A$ structure of the Standard Model. Modifications of
the rates and angular asymmetries which arise at next-to-leading order are
discussed. Measurements for $\Lambda_b \to \Lambda \gamma$ and the CP conjugate
mode, with branching ratios of a few times $10^{-5}$, are shown to be sensitive
to non-standard sources of CP violation in the $\Lambda_b \to \Lambda \gamma$
matrix element. Form factor relations for heavy-to-light baryon decays are
derived in the large energy limit, which are of general interest.
