Accessing CKM suppressed top decays at the LHC

Abstract

We present an strategy for measuring the off-diagonal elements of the third row of CKM matrix $|V_{tq}|$ through the branching fractions of top quark decays $t\to q W$, where $q$ is a light quark jet. This strategy is an extension of existing measurements, with the improvement rooted in the use of orthogonal $b$- and $q$-taggers that add a new observable, the number of light-quark-tagged jets, to the already commonly used observable, the fraction of $b$-tagged jets in an event. Careful inclusion of the additional complementary observable significantly increases the expected statistical power of the analysis, with the possibility of excluding a null $|V_{td}|^2+|V_{ts}|^2$ at $95\%$ C.L. at the HL-LHC.