Signatures of Invisible Fermions in ${\Lambda }_b^0\to {\Lambda }_c^{+}{\ell }^{-}{\bar{X}}_{\mathrm{inv}}$ Decays

Abstract

We investigate the effects of a massive invisible fermion in ${\Lambda }_b^0\to {\Lambda }_c^{+}{\ell }^{-}{\bar{X}}_{\mathrm{inv}}$ decays using a model-independent weak effective theory. Through a comprehensive angular analysis, we show that a nonzero invisible-particle mass leaves characteristic imprints on angular observables that can distinguish massless and massive invisible states. We further demonstrate that these observables provide strong discrimination among vector/axial-vector, scalar/pseudoscalar, and tensor interactions, as well as between left- and right-handed quark and lepton current operators.

19 pages, 3 figures, and 2 tables