Probing for new physics in polarizedΛbdecays at theZpole

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 $\overrightarrow{b}s\gamma$ dipole operators. Comparison with the $\Lambda$ decay polarization asymmetry and with the ${\Lambda }_b$ polarization extracted from semileptonic decays allows important tests of the $V-A$ structure of the standard model. The modifications of the rates and angular asymmetries which arise at next-to-leading order are discussed. The measurements for ${\Lambda }_b\to \Lambda \gamma$ and the $\mathrm{CP}$ conjugate mode, with branching ratios of a few times ${10}^{-5},$ are shown to be sensitive to nonstandard sources of $\mathrm{CP}$ 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.