Measuring the Magnitude of the Fourth-Generation CKM4 Matrix Element V_{t'b'}

Understand

We study the decays of heavy chiral (t', b') quarks in a four-generation extension of the Standard Model.

• If the difference between the t' and b' masses is smaller than the W mass, as favored by precision electroweak measurements, then the Cabibbo-Kobayashi-Maskawa favored, on-shell decay t'-->b'W is forbidden.
• As a result, other t' decays have substantial branching fractions, which are highly sensitive to the magnitude of the diagonal CKM matrix element V_{t'b'}.
• We show that |V_{t'b'}| can be determined from the ratio of the two-body and three-body t'-decay branching fractions and estimate the precision of such a measurement at the LHC.