Measurement of missing transverse energy in top pair events

A differential cross section measurement of top quark pair production with missing transverse energy is presented using 5.1~fb$^{-1}$ of data collected using the CMS detector at the LHC at a centre of mass energy of 7~TeV. The analysis selects events with a single isolated high energy electron or muon, which is assumed to come from one of the W bosons produced in the decays of the top quark and antiquark. The differential cross section is measured in bins of missing transverse energy. The results are consistent with the predictions of simulation.