Accessing CKM suppressed top decays at the LHC

Abstract

We propose an extension of the existing experimental strategy for measuring branching fractions of top quark decays, targeting specifically t\to j_q Wt→jqW, where j_qjq is a light quark jet. The improved strategy uses orthogonal bb- and qq-taggers, and adds a new observable, the number of light-quark-tagged jets, to the already commonly used observable, the fraction of bb-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 |V_{tb}|=1|Vtb|=1 at 95\%95% C.L. at the HL-LHC, and accessing directly the standard model value of |V_{td}|^2+|V_{ts}|^2|Vtd|2+|Vts|2.