Measurement of the shape of the $Lambda_b^0toLambda_c^+ mu^- overline{ u}$ differential decay rate

A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay $Lambda_b^0toLambda_c^+mu^-overline{ u}$ is reported, using data corresponding to $3 fb^{-1}$ collected with the LHCb detector in proton-proton collisions. The $Lambda_c^+mu^-overline{ u}$(+ anything) final states are reconstructed through the detection of a muon and a $Lambda_c^+$ baryon decaying into $pK^-pi^+$, and the decays $Lambda_b^0toLambda_c^+pi^+pi^-mu^-overline{ u}$ are used to determine contributions from $Lambda_b^0to Lambda_c^{star+}mu ^-bar{ u}$ decays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, $q^2$, is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.