Measurement of the CKM matrix element | V_cb| 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→ cb¯ , where the source of the real W bosons is the abundant tt¯ sample. By applying b-tagging algorithms on jets from W→ qq¯ ^′, we can measure the fraction of W→ cb¯ present. With approximately 300fb-1 of data, the significance is large enough to merit further development of the method.