Measurement of the CKM matrix element |Vcb| from top quark pair events at the LHC

Measurements of the Cabbibo-Kobayashi-Maskawa matrix elements are important tests of the consistency of the standard model. However, there is some tension in the |V-cb| measurements, depending on the final states used. The |V-cb has been determined from the measured branching ratios of a B-hadron to final states with c quarks. An independent method of measuring |V-cb| is needed to understand the cause of the discrepancies. We propose a new way of measuring |V-cb at the LHC. It can be measured from decay of real W bosons W -> c (b) over bar, where the source of the real W bosons is the abundant t (t) over bar sample. By applying b-tagging algorithms on jets from W -> q (q) over bar, we can measure the fraction of W -> c (b) over bar present. With approximately 300 fb(-1) of data, the significance is large enough to merit further development of the method.