Probing for new physics in polarized Λb decays at the Z pole -: art. no. 074038

Polarized Lambda(b)-->Lambdagamma 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-->sgamma 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)-->Lambdagamma and the CP conjugate mode, with branching ratios of a few times 10(-5), are shown to be sensitive to nonstandard sources of CP violation in the Lambda(b)-->Lambdagamma matrix element. Form factor relations for heavy-to-light baryon decays are derived in the large energy limit, which are of general interest.