The first paragraph on p. 15 of the original version should be replaced by the following paragraph, which deletes an incorrect reference to a figure.The uncertainties on the mistagged NTMJ background include the statistical uncertainty on the sample after loose selection, to which the mistag probability is applied; the statistical uncertainty on the mistag probability itself, ranging from <1% at 1 TeV/c 2 to ≈10% at 3 TeV/c 2 ; and the systematic uncertainty on the mistag probability application, as described in section 3.3, which is in the range of 1 to 5% depending on the t t mass.The total background uncertainty is ≈5% for the low-mass region, dominated by the systematic uncertainty, and ≈100% for the high-mass region, dominated by statistical uncertainty associated with the sample after loose selection.